+
1.8) What documentation is available for PostgreSQL?
+A user manual, manual pages, and some small test examples are included
+in the distribution. The sql and built-in manual pages are particularly
+important.
+The www page contains pointers to an implementation guide and five
+papers written about postgres design concepts and features.
+
1.9) What version of SQL does PostgreSQL use?
+PostgreSQL supports a subset of SQL-92. It has most of the important
+constructs but lacks some of the functionality. The most visible
+differences are:
+
no support for nested subqueries
+
no HAVING clause under a GROUP BY
+
+On the other hand, you get to create user-defined types, functions,
+inheritance etc. If you're willing to help with PostgreSQL coding,
+eventually we can also add the missing features listed above.
+
1.10) Does PostgreSQL work with databases from
+earlier versions of postgres?
+PostgreSQL v1.09 is compatible with databases created with v1.01. Those
+upgrading from 1.0 should read the directions in the
+MIGRATION_1.0_TO_1.02 directory.
+Upgrading to 6.0 requires a dump and restore from previous releases.
+Upgrading to 6.1 requires a dump and restore from previous releases.
+Those ugrading from versions earlier than 1.09 must upgrade to 1.09
+first without a dump/reload, then dump the data from 1.09, and then load
+it into 6.0 or 6.1.
+
1.11) How many people use PostgreSQL?
+Since we don't have any licensing or registration scheme, it's
+impossible to tell. We do know hundreds copies of PostgreSQL v1.* have
+been downloaded, and that there many hundreds of subscribers to the
+mailing lists.
+
+
Section 2: Installation Questions
+
+
check to see that you have the proper paths set
+
check that the 'postgres' user owns all the right files
+
ensure that there are files in $PGDATA/files, and that they
+are non-empty. If they aren't, then "gmake install" failed for
+some reason
+
+
2.2) when I start up the postmaster, I get
+ "FindBackend: could not find a backend to execute..."
+ "postmaster: could not find backend to execute..."
+You probably do not have the right path set up. The 'postgres'
+executable needs to be in your path.
+
2.3) The system seems to be confused about commas,
+decimal points, and date formats.
+Check your locale configuration. PostgreSQL uses the locale settings of
+the user that ran the postmaster process. Set those accordingly for
+your operating environment.
+
2.4) How do I install PostgreSQL somewhere other than
+/usr/local/pgsql?
+You need to edit Makefile.global and change POSTGRESDIR accordingly, or
+create a Makefile.custom and define POSTGRESDIR there.
+
2.5) When I run postmaster, I get a Bad System
+Call core dumped message.
+It could be a variety of problems, but first check to see that you have
+system V extensions installed on your kernel. PostgreSQL requires kernel
+support for shared memory.
+
2.6) When I try to start the postmaster, I get
+IpcMemoryCreate errors.
+You either do not have shared memory configured properly in kernel or
+you need to enlarge the shared memory available in the kernel. The
+exact amount you need depends on your architecture and how many buffers
+you configure postmaster to run with. For most systems, with default
+buffer sizes, you need a minimum of ~760K.
+
2.7) I have changed a source file, but a
+recompile does not see the change?
+The Makefiles do not have the proper dependencies for include files. You
+have to do a 'make clean' and then another 'make'.
+
+
Section 3: PostgreSQL Features
+
- 1.1) What is PostgreSQL?
-
- PostgreSQL is an enhancement of the POSTGRES database management
- system, a next-generation DBMS research prototype. While PostgreSQL
- retains the powerful data model and rich data types of POSTGRES, it
- replaces the PostQuel query language with an extended subset of SQL.
- PostgreSQL is free and the complete source is available.
-
- PostgreSQL development is being performed by a team of Internet
- developers who all subscribe to the PostgreSQL development mailing
- list. The current coordinator is Marc G. Fournier
- responsible for all current and future development of PostgreSQL.
-
- The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
- others have contributed to the porting, testing, debugging and
- enhancement of the code. The original Postgres code, from which
- PostgreSQL is derived, was the effort of many graduate students,
- undergraduate students, and staff programmers working under the
- direction of Professor Michael Stonebraker at the University of
- California, Berkeley.
-
- The original name of the software at Berkeley was Postgres. When SQL
- functionality was added in 1995, its name was changed to Postgres95.
- The name was changed at the end of 1996 to PostgreSQL.
-
- 1.2) What does PostgreSQL run on?
-
- The authors have compiled and tested PostgreSQL on the following
- platforms(some of these compiles require gcc 2.7.0):
- * aix - IBM on AIX 3.2.5
- * alpha - DEC Alpha AXP on OSF/1 2.0
- * BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
- * bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0
- * dgux - DG/UX 5.4R3.10
- * hpux - HP PA-RISC on HP-UX 9.0
- * i386_solaris - i386 Solaris
- * irix5 - SGI MIPS on IRIX 5.3
- * linux - Intel x86 on Linux 1.2 and Linux ELF (For non-ELF Linux,
- see LINUX_ELF below).
- * sparc_solaris - SUN SPARC on Solaris 2.4
- * sunos4 - SUN SPARC on SunOS 4.1.3
- * svr4 - Intel x86 on Intel SVR4
- * ultrix4 - DEC MIPS on Ultrix 4.4
-
- The following platforms have known problems/bugs:
- * nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2
-
- 1.3) Where can I get PostgreSQL?
-
- The primary anonymous ftp site for PostgreSQL is:
- * ftp://ftp.postgreSQL.org/pub
-
- A mirror site exists at:
- * ftp://postgres95.vnet.net/pub/postgres95
- * ftp://ftp.luga.or.at/pub/postgres95
- * ftp://cal011111.student.utwente.nl/pub/postgres95
- * ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95
- * ftp://rocker.sch.bme.hu
-
- 1.4) What's the copyright on PostgreSQL?
-
- PostgreSQL is subject to the following COPYRIGHT.
-
- PostgreSQL Data Base Management System
-
- Copyright (c) 1994-6 Regents of the University of California
-
- Permission to use, copy, modify, and distribute this software and its
- documentation for any purpose, without fee, and without a written
- agreement is hereby granted, provided that the above copyright notice
- and this paragraph and the following two paragraphs appear in all
- copies.
-
- IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
- FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
- INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND
- ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN
- ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
- THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
- INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
- MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
- PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
- CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT,
- UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
-
- 1.5) Support for PostgreSQL
-
- There is no official support for PostgreSQL from the original
- maintainers or from University of California, Berkeley. It is
- maintained through volunteer effort only.
-
- for discussion o f matters pertaining to PostgreSQL, including but not
- limited to bug reports and fixes. For info on how to subscribe, send a
- mail with the lines in the body (not the subject line)
-
-
- subscribe
- end
-
-
- There is also a digest list available. To subscribe to this list, send
-
-
- subscribe
- end
-
- Digests are sent out to members of this list whenever the main list
- has received around 30k of messages.
-
- There is a bugs mailing list available. To subscribe to this list,
-
- There is also a developers discussion mailing list available. To
- with a BODY of:
-
-
- subscribe
- end
-
- Additional information about PostgreSQL can be found via the
- PostgreSQL WWW home page at:
-
- http://postgreSQL.org
-
- 1.6) Latest release of PostgreSQL
-
- The latest release of PostgreSQL is version 6.0, which was released on
- January 31, 1997. 6.1 is scheduled for release soon. For information
- about what is new in 6.1, see our TODO list on our WWW page.
-
- We expect a 7.0 release in several months that will remove time-travel
- and reduce by 50% the size of on-disk system columns maintained for
- each row in a table. This release will also require a dump and
- restore.
-
- 1.7) Is there a commercial version of PostgreSQL?
-
- Illustra Information Technology (a wholly owned subsidiary of Informix
- Software, Inc.) sells an object-relational DBMS called Illustra that
- was originally based on postgres. Illustra has cosmetic similarities
- to PostgreSQL but has more features, is more robust, performs better,
- and offers real documentation and support. On the flip side, it costs
-
- 1.8) What documentation is available for PostgreSQL?
-
- A user manual, manual pages, and some small test examples are included
- in the distribution. The sql and built-in manual pages are
- particularly important.
-
- The www page contains pointers to an implementation guide and five
- papers written about postgres design concepts and features.
-
- 1.9) What version of SQL does PostgreSQL use?
-
- PostgreSQL supports a subset of SQL-92. It has most of the important
- constructs but lacks some of the functionality. The most visible
- differences are:
- * no support for nested subqueries
- * no HAVING clause under a GROUP BY
-
- On the other hand, you get to create user-defined types, functions,
- inheritance etc. If you're willing to help with PostgreSQL coding,
- eventually we can also add the missing features listed above.
-
- 1.10) Does PostgreSQL work with databases from earlier versions of postgres?
-
- PostgreSQL v1.09 is compatible with databases created with v1.01.
- Those upgrading from 1.0 should read the directions in the
- MIGRATION_1.0_TO_1.02 directory.
-
- Upgrading to 6.0 requires a dump and restore from previous releases.
-
- 1.11) How many people use PostgreSQL?
-
- Since we don't have any licensing or registration scheme, it's
- impossible to tell. We do know hundreds copies of PostgreSQL v1.* have
- been downloaded, and that there many hundreds of subscribers to the
- mailing lists.
-
- _________________________________________________________________
-
-Section 2: Installation Questions
-
- 2.1) initdb doesn't run
-
- * check to see that you have the proper paths set
- * check that the 'postgres' user owns all the right files
- * ensure that there are files in $PGDATA/files, and that they are
- non-empty. If they aren't, then "gmake install" failed for some
- reason
-
- 2.2) when I start up the postmaster, I get "FindBackend: could not find a
- backend to execute..." "postmaster: could not find backend to execute..."
-
- You probably do not have the right path set up. The 'postgres'
- executable needs to be in your path.
-
- 2.3) The system seems to be confused about commas, decimal points, and date
- formats.
-
- Check your locale configuration. PostgreSQL uses the locale settings
- of the user that ran the postmaster process. Set those accordingly for
- your operating environment.
-
- 2.4) How do I install PostgreSQL somewhere other than /usr/local/pgsql?
-
- You need to edit Makefile.global and change POSTGRESDIR accordingly,
- or create a Makefile.custom and define POSTGRESDIR there.
-
- 2.5) When I run postmaster, I get a Bad System Call core dumped message.
-
- It could be a variety of problems, but first check to see that you
- have system V extensions installed on your kernel. PostgreSQL requires
- kernel support for shared memory.
-
- 2.6) I get the error message "obj/fmgr.h: No such file or directory"
-
- This indicates that you did not generate the file fmgr.h properly.
- Something failed in the running of the
- src/backend/utils/Gen_fmgrtab.sh script. Check to see the paths used
- in that script is appropriate to your system.
-
- 2.7) When I try to start the postmaster, I get IpcMemoryCreate errors.
-
- You either do not have shared memory configured properly in kernel or
- you need to enlarge the shared memory available in the kernel. The
- exact amount you need depends on your architecture and how many
- buffers you configure postmaster to run with. For most systems, with
- default buffer sizes, you need a minimum of ~760K.
-
- 2.8) I have changed a source file, but a recompile does not see the change?
-
- The Makefiles do not have the proper dependencies for include files.
- You have to do a 'make clean' and then another 'make'.
-
- _________________________________________________________________
-
-Section 3: PostgreSQL Features
-
- 3.1) How do I specify a KEY or other constraints on a column?
-
- Column constraints are not supported in PostgreSQL. As a consequence,
- the system does not check for duplicates.
-
- Under 6.0, create a unique index on the column. Attempts to create
- duplicate of that column will report an error.
-
- 3.2) Does PostgreSQL support nested subqueries?
-
- Subqueries are not implemented, but they can be simulated using sql
- functions.
-
- 3.3) How do I define a unique indices?
-
- PostgreSQL 6.0 supports unique indices.
-
- 3.4) I've having a lot of problems using rules.
-
- Currently, the rule system in PostgreSQL is mostly broken. It works
- enough to support the view mechanism, but that's about it. Use
- PostgreSQL rules at your own peril.
-
- 3.5) I can't seem to write into the middle of large objects reliably.
-
- The Inversion large object system in PostgreSQL is also mostly broken.
- It works well enough for storing large wads of data and reading them
- back out, but the implementation has some underlying problems. Use
- PostgreSQL large objects at your own peril.
-
- 3.6) Does PostgreSQL have a graphical user interface? A report generator? A
- embedded query language interface?
-
- No. No. No. Not in the official distribution at least. Some users have
- reported some success at using 'pgbrowse' and 'onyx' as frontends to
- PostgreSQL. Several contributions are working on tk based frontend
- tools. Ask on the mailing list.
-
- 3.7) How can I write client applications to PostgreSQL?
-
- PostgreSQL supports a C-callable library interface called libpq as
- well as a Tcl-based library interface called libtcl.
-
- Others have contributed a perl interface and a WWW gateway to
- PostgreSQL. See the PostgreSQL home pages for more details.
-
- 3.8) How do I prevent other hosts from accessing my PostgreSQL backend?
-
- Use host-based authentication by modifying the file $PGDATA/pg_hba
- accordingly.
-
- 3.9) How do I set up a pg_group?
-
- Currently, there is no easy interface to set up user groups. You have
- to explicitly insert/update the pg_group table. For example:
-
-
- jolly=> insert into pg_group (groname, grosysid, grolist)
- jolly=> values ('posthackers', '1234', '{5443, 8261}');
- INSERT 548224
- jolly=> grant insert on foo to group posthackers;
- CHANGE
- jolly=>
-
- The fields in pg_group are:
- * groname: the group name. This a char16 and should be purely
- alphanumeric. Do not include underscores or other punctuation.
- * grosysid: the group id. This is an int4. This should be unique for
- each group.
- * grolist: the list of pg_user id's that belong in the group. This
- is an int4[].
-
- 3.10) What is the exact difference between binary cursors and normal cursors?
-
- Normal cursors return data back in ASCII format. Since data is stored
- natively in binary format, the system must do a conversion to produce
- the ASCII format. In addition, ASCII formats are often large in size
- than binary format. Once the attributes come back in ASCII, often the
- client application then has to convert it to a binary format to
- manipulate it anyway.
-
- Binary cursors give you back the data in the native binary
- representation. Thus, binary cursors will tend to be a little faster
- since there's less overhead of conversion.
-
- However, ASCII is architectural neutral whereas binary representation
- can differ between different machine architecture. Thus, if your
- client machine uses a different representation than you server
- machine, getting back attributes in binary format is probably not what
- you want. Also, if your main purpose is displaying the data in ASCII,
- then getting it back in ASCII will save you some effort on the client
- side.
-
- 3.11) Why doesn't the != operator work?
-
- SQL specifies <> as the inequality operator, and that is what we have
- defined for the built-in types.
-
- In 6.0, != is equivalent to <>.
-
- 3.12) What is a R-tree index and what is it used for?
-
- An r-tree index is used for indexing spatial data. A hash index can't
- handle range searches. A B-tree index only handles range searches in a
- single dimension. R-tree's can handle multi-dimensional data. For
- example, if a R-tree index can be built on an attribute of type
- 'point', the system can more efficient answer queries like select all
- points within a bounding rectangle.
-
- The canonical paper that describes the original R-Tree design is:
-
- Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial
- Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data,
- 45-57.
-
- You can also find this paper in Stonebraker's "Readings in Database
- Systems"
-
- 3.13) What is the maximum size for a tuple?
-
- Tuples are limited to 8K bytes. Taking into account system attributes
- and other overhead, one should stay well shy of 8,000 bytes to be on
- the safe side. To use attributes larger than 8K, try using the large
- objects interface.
-
- Tuples do not cross 8k boundaries so a 5k tuple will require 8k of
- storage.
-
- 3.14) I defined indices but my queries don't seem to make use of them. Why?
-
- PostgreSQL does not automatically maintain statistics. One has to make
- an explicit 'vacuum' call to update the statistics. After statistics
- are updated, the optimizer has a better shot at using indices. Note
- that the optimizer is limited and does not use indices in some
- circumstances (such as OR clauses).
-
- If the system still does not see the index, it is probably because you
- have created an index on a field with the improper *_ops type. For
- example, you have created a CHAR(4) field, but have specified a
- char_ops index type_class.
-
- See the create_index manual page for information on what type classes
- are available. It must match the field type.
-
- Postgres does not warn the user when the improper index is created.
-
- Indexes not used for ORDER BY operations.
-
- 3.15) Are there ODBC drivers for PostgreSQL?
-
- There are two ODBC drivers available, PostODBC and OpenLink ODBC.
-
- For all people being interested in PostODBC, there are now two mailing
- lists devoted to the discussion of PostODBC. The mailing lists are:
- * postodbc-developers@listse rv.direct.net
-
- these lists are ordinary majordomo mailing lists. You can subscribe by
- sending a mail to:
-
- OpenLink ODBC is currently in beta under Linux. You can get it from
- http://www.openlinksw.com/postgres.html. It works with our standard
- ODBC client software so you'll have Postgres ODBC available on every
- client platform we support (Win, Mac, Unix, VMS).
-
- We will probably be selling this product to people who need
- commercial-quality support, but a freeware version will always be
-
- 3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
-
- Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
- be extended to handle higher number of dimensions. In practice,
- extending R-trees require a bit of work and we don't currently have
- any documentation on how to do it.
-
- 3.17) How do I do regular expression searches? case-insensitive regexp
- searching?
-
- PostgreSQL supports the SQL LIKE syntax as well as more general
- regular expression searching with the ~ operator. The !~ is the
- negated regexp operator. ~* and !~* are the case-insensitive regular
- expression operators.
-
- 3.18) I can't access the database as the 'root' user.
-
- You should not create database users with user id 0(root). They will
- be unable to access the database. This is a security precaution
- because of the ability of any user to dynamically link object modules
- into the database engine.
-
- 3.19) I experienced a server crash during a vacuum. How do I remove the lock
- file?
-
- If the server crashes during a vacuum command, chances are it will
- leave a lock file hanging around. Attempts to re-run the vacuum
- command result in
-
-
- WARN:can't create lock file -- another vacuum cleaner running?
-
- If you are sure that no vacuum is actually running, you can remove the
- file called "pg_vlock" in your database directory (which is
- $PGDATA/base/)
-
- 3.20) What is the difference between the various character types?
-
+
3.1) How do I specify a KEY or other constraints on a
+column?
+Column constraints are not supported in PostgreSQL. As a consequence,
+the system does not check for duplicates.
+Under 6.0, create a unique index on the column. Attempts to create
+duplicate of that column will report an error.
+
3.2) Does PostgreSQL support nested subqueries?
+Subqueries are not implemented, but they can be simulated using sql
+functions.
+
3.3) How do I define a unique indices?
+PostgreSQL 6.0 supports unique indices.
+
3.4) I've having a lot of problems using rules.
+Currently, the rule system in PostgreSQL is mostly broken. It works
+enough to support the view mechanism, but that's about it. Use
+PostgreSQL rules at your own peril.
+
3.5) I can't seem to write into the middle of large
+objects reliably.
+The Inversion large object system in PostgreSQL is also mostly broken.
+It works well enough for storing large wads of data and reading them
+back out, but the implementation has some underlying problems. Use
+PostgreSQL large objects at your own peril.
+
3.6) Does PostgreSQL have a graphical user interface?
+A report generator? A embedded query language interface?
+No. No. No. Not in the official distribution at least. Some users have
+reported some success at using 'pgbrowse' and 'onyx' as frontends to
+PostgreSQL. Several contributions are working on tk based frontend
+tools. Ask on the mailing list.
+
3.7) How can I write client applications to PostgreSQL?
+PostgreSQL supports a C-callable library interface called libpq as well
+as a Tcl-based library interface called libtcl.
+Others have contributed a perl interface and a WWW gateway to
+PostgreSQL. See the PostgreSQL home pages for more details.
+
3.8) How do I prevent other hosts from accessing my
+PostgreSQL backend?
+Use host-based authentication by modifying the file $PGDATA/pg_hba
+accordingly.
+
3.9) How do I set up a pg_group?
+Currently, there is no easy interface to set up user groups. You have to
+explicitly insert/update the pg_group table. For example:
+
+ jolly=> insert into pg_group (groname, grosysid, grolist)
+ jolly=> values ('posthackers', '1234', '{5443, 8261}');
+ INSERT 548224
+ jolly=> grant insert on foo to group posthackers;
+ CHANGE
+ jolly=>
+
+
+ The fields in pg_group are:
+
groname: the group name. This a char16 and should
+ be purely alphanumeric. Do not include underscores
+ or other punctuation.
+
grosysid: the group id. This is an int4.
+ This should be unique for each group.
+
grolist: the list of pg_user id's that belong in the group.
+ This is an int4[].
+
+
3.10) What is the exact difference between binary
+cursors and normal cursors?
+Normal cursors return data back in ASCII format. Since data is stored
+natively in binary format, the system must do a conversion to produce
+the ASCII format. In addition, ASCII formats are often large in size
+than binary format. Once the attributes come back in ASCII, often the
+client application then has to convert it to a binary format to
+manipulate it anyway.
+Binary cursors give you back the data in the native binary
+representation. Thus, binary cursors will tend to be a little faster
+since there's less overhead of conversion.
+However, ASCII is architectural neutral whereas binary representation
+can differ between different machine architecture. Thus, if your client
+machine uses a different representation than you server machine, getting
+back attributes in binary format is probably not what you want. Also, if
+your main purpose is displaying the data in ASCII, then getting it back
+in ASCII will save you some effort on the client side.
+
3.11) Why doesn't the != operator work?
+SQL specifies <> as the inequality operator, and that is what we
+have defined for the built-in types.
+In 6.0, != is equivalent to <>.
+
3.12) What is a R-tree index and what is it used for?
+An r-tree index is used for indexing spatial data. A hash index can't
+handle range searches. A B-tree index only handles range searches in a
+single dimension. R-tree's can handle multi-dimensional data. For
+example, if a R-tree index can be built on an attribute of type 'point',
+the system can more efficient answer queries like select all points
+within a bounding rectangle.
+The canonical paper that describes the original R-Tree design is:
+Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
+Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
+You can also find this paper in Stonebraker's "Readings in Database
+Systems"
+
3.13) What is the maximum size for a tuple?
+Tuples are limited to 8K bytes. Taking into account system attributes
+and other overhead, one should stay well shy of 8,000 bytes to be on the
+safe side. To use attributes larger than 8K, try using the large
+objects interface.
+Tuples do not cross 8k boundaries so a 5k tuple will require 8k of
+storage.
+
3.14) I defined indices but my queries don't seem
+to make use of them. Why?
+PostgreSQL does not automatically maintain statistics. One has to make
+an explicit 'vacuum' call to update the statistics. After statistics
+are updated, the optimizer has a better shot at using indices. Note
+that the optimizer is limited and does not use indices in some
+circumstances (such as OR clauses).
+If the system still does not see the index, it is probably because you
+have created an index on a field with the improper *_ops type. For
+example, you have created a CHAR(4) field, but have specified a char_ops
+index type_class.
+See the create_index manual page for information on what type classes
+are available. It must match the field type.
+Postgres does not warn the user when the improper index is created.
+Indexes not used for ORDER BY operations.
+
3.15) Are there ODBC drivers for PostgreSQL?
+There are two ODBC drivers available, PostODBC and OpenLink ODBC.
+For all people being interested in PostODBC, there are now two mailing
+lists devoted to the discussion of PostODBC. The mailing lists are:
+
+net
+
+rv.direct.net
+
+these lists are ordinary majordomo mailing lists. You can subscribe by
+sending a mail to:
+
+
+OpenLink ODBC is currently in beta under Linux. You can get it from
+href="http://www.openlinksw.com/postgres.html">
+http://www.openlinksw.com/postgres.html. It works with our standard
+ODBC client software so you'll have Postgres ODBC available on every
+client platform we support (Win, Mac, Unix, VMS).
+We will probably be selling this product to people who need
+commercial-quality support, but a freeware version will always be
+available. Questions to
+
3.16) How do I use postgres for multi-dimensional
+indexing (> 2 dimensions)?
+Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
+be extended to handle higher number of dimensions. In practice,
+extending R-trees require a bit of work and we don't currently have any
+documentation on how to do it.
+
3.17) How do I do regular expression searches?
+case-insensitive regexp searching?
+PostgreSQL supports the SQL LIKE syntax as well as more general regular
+expression searching with the ~ operator. The !~ is the negated regexp
+operator. ~* and !~* are the case-insensitive regular expression
+operators.
+
3.18) I can't access the database as the 'root' user.
+You should not create database users with user id 0(root). They will be
+unable to access the database. This is a security precaution because
+of the ability of any user to dynamically link object modules into the
+database engine.
+
3.19) I experienced a server crash during a
+vacuum. How do I remove the lock file?
+If the server crashes during a vacuum command, chances are it will leave
+a lock file hanging around. Attempts to re-run the vacuum command
+result in
+
+ WARN:can't create lock file -- another vacuum cleaner running?
+
+
+If you are sure that no vacuum is actually running, you can remove the
+file called "pg_vlock" in your database directory (which is
+$PGDATA/base/<dbName>)
+
3.20) What is the difference between the various
+character types?
Type Internal Name Notes
--------------------------------------------------
CHAR char 1 character }
VARCHAR(#) varchar size specifies maximum length, no padding
TEXT text length limited only by maximum tuple length
BYTEA bytea variable-length array of bytes
+
+Remember, you need to use the internal name when creating indexes on
+these fields or when doing other internal operations.
+The last four types above are "varlena" types (i.e. the first four bytes
+is the length, followed by the data). CHAR(#) and VARCHAR(#) allocate
+the maximum number of bytes no matter how much data is stored in the
+field. TEXT and BYTEA are the only character types that have variable
+length on the disk.
+
3.21) In a query, how do I detect if a field is NULL?
+PostgreSQL has two builtin keywords, "isnull" and "notnull" (note no
+spaces). Version 1.05 and later and 6.* understand IS NULL and IS NOT
+NULL.
+
3.22) How do I see how the query optimizer is
+evaluating my query?
+Place the word 'EXPLAIN' at the beginning of the query, for example:
+
+ EXPLAIN SELECT * FROM table1 WHERE age = 23;
+
+
+
3.23) How do I create a serial field?
+Postgres does not allow the user to specifiy a user column as type
+SERIAL. Instead, you can use each row's oid field as a unique value.
+However, if you need to dump and reload the database, you need to be
+using postgres version 1.07 or later or 6.* with pgdump's -o option or
+COPY's WITH OIDS option to preserver the oids.
+Another valid way of doing this is to create a function:
+
+ create table my_oids (f1 int4);
+ insert into my_oids values (1);
+ create function new_oid () returns int4 as
+ 'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
+ language 'sql';
+
+
+then:
+
+ create table my_stuff (my_key int4, value text);
+ insert into my_stuff values (new_oid(), 'hello');
+
+
+However, keep in mind there is a race condition here where one server
+could do the update, then another one do an update, and they both could
+select the same new id. This statement should be performed within a
+transaction.
+Sequences are implemented in 6.1
+
3.24) How do I create a multi-column index?
- Remember, you need to use the internal name when creating indexes on
- these fields or when doing other internal operations.
-
- The last four types above are "varlena" types (i.e. the first four
- bytes is the length, followed by the data). CHAR(#) and VARCHAR(#)
- allocate the maximum number of bytes no matter how much data is stored
- in the field. TEXT and BYTEA are the only character types that have
- variable length on the disk.
-
- 3.21) In a query, how do I detect if a field is NULL?
-
- PostgreSQL has two builtin keywords, "isnull" and "notnull" (note no
- spaces). Version 1.05 and later and 6.* understand IS NULL and IS NOT
- NULL.
-
- 3.22) How do I see how the query optimizer is evaluating my query?
-
- Place the word 'EXPLAIN' at the beginning of the query, for example:
-
- EXPLAIN SELECT * FROM table1 WHERE age = 23;
-
- 3.23) How do I create a serial field?
-
- Postgres does not allow the user to specifiy a user column as type
- SERIAL. Instead, you can use each row's oid field as a unique value.
- However, if you need to dump and reload the database, you need to be
- using postgres version 1.07 or later or 6.* with pgdump's -o option or
- COPY's WITH OIDS option to preserver the oids.
-
- Another valid way of doing this is to create a function:
-
- create table my_oids (f1 int4);
- insert into my_oids values (1);
- create function new_oid () returns int4 as
- 'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
- language 'sql';
-
- then:
-
- create table my_stuff (my_key int4, value text);
- insert into my_stuff values (new_oid(), 'hello');
-
- However, keep in mind there is a race condition here where one server
- could do the update, then another one do an update, and they both
- could select the same new id. This statement should be performed
- within a transaction.
-
- 3.24) How do I create a multi-column index?
-
- In 6.0, you can not directly create a multi-column index using create
- index. You need to define a function which acts on the multiple
- columns, then use create index with that function.
-
- In 6.1, this feature is available.
-
- 3.25) What are the temp_XXX files in my database directory?
-
- They are temp_ files generated by the query executor. For example, if
- a sort needs to be done to satisfy an ORDER BY, some temp files are
- generated as a result of the sort.
-
- If you have no transactions or sorts running at the time, it is safe
- to delete the temp_ files.
-
- 3.26) Why are my table files not getting any smaller after a delete?
-
- If you run vacuum in pre-6.0, unused rows will be marked for reuse,
- but the file blocks are not released.
-
- In 6.0, vacuum properly shrinks tables.
-
- 3.27) Why can't I connect to my database from another machine?
-
- The default configuration allows only connections from tcp/ip host
- localhost. You need to add a host entry to the file pgsql/data/pg_hba.
-
- 3.28) I get the error 'default index class unsupported' when creating an
- index. How do I do it?
-
- You probably used:
-
- create index idx1 on person using btree (name);
-
- PostgreSQL indexes are extensible, and therefore in pre-6.0, you must
- specify a class_type when creating an index. Read the manual page for
- create index (called create_index).
-
- Version 6.0, if you do not specify a class_type, it defaults to the
- proper type for the column.
-
- 3.29) Why does creating an index crash the backend server?
-
- You have probably defined an incorrect *_ops type class for the field
- you are indexing.
-
- 3.30) How do I specify a decimal constant as a float8, or a string as a text?
- Why am I getting poor precision?
-
- Use the :: operator. It is needed only when the default promotion
- rules fail. i.e.:
-
-
- insert into tab1 values (4.23::float8, '2343'::text)
-
- The default floating-point constant is a float4 in releases prior to
- 1.05. Later releases default to float8.
-
- 3.31) How do I find out what indexes or operations are defined in the
- database?
-
- Run the file pgsql/src/tutorial/syscat.source. It illustrates many of
- the 'select's needed to get information out of the database system
- tables.
-
- 3.32) My database is corrupt. I can't do anything. What should I do?
-
- The 1.02 release has a README file and utility that describes a
- possible cause of the problem and a workaround.
-
- This bug is fixed in 1.02.1.
-
- 3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
-
- Release 1.02 does not have this problem.
-
- The 1.01 release of PostgreSQL uses a variable called PAGER to filter
- the output of SELECT statements. Unfortunately, this PAGER is used
- even when the standard output is not a terminal.
-
- 3.34) Why do statements require an extra character at the end? Why does
- 'createuser' return 'unexpected last match in input()'? Why does pg_dump
- fail?
-
- You have compile postgres with flex version 2.5.3. There is bug in
- this version of flex. Use flex version 2.5.2 or flex 2.5.4 instead.
- There is a doc/README.flex file which will properly patch the flex
- 2.5.3 source code.
-
- 3.35) All my servers crash under concurrent table access. Why?
-
- This problem can be caused by a kernel that is not configured to
- support semaphores.
-
- 3.36) What tools are available for hooking postgres to Web pages?
-
- For web integration, PHP/FI is an excellent interface. The URL for
- that is http://www.vex.net/php/
-
- PHP is great for simple stuff, but for more complex stuff, some still
- use the perl interface and CGI.pm.
-
- An example of using WWW with C to talk to Postgres is can be tried at:
- * http://postgreSQL.org/~mlc
-
- An WWW gatway based on WDB using perl can be downloaded from:
- * http://www.eol.ists.ca/~dunlop/wdb -p95
-
- 3.37) What is the time-warp feature and how does it relate to vacuum?
-
- PostgreSQL handles data changes differently than most database
- systems. When a row is changed in a table, the original row is marked
- with the time it was changed, and a new row is created with the
- current data. By default, only current rows are used in a table. If
- you specify a date/time after the table name in a FROM clause, you can
- access the data that was current at that time, i.e.
-
-
- SELECT *
- FROM employees ['July 24, 1996 09:00:00']
-
- displays employee rows in the table at the specified time. You can
- specify intervals like [date,date], [date,], [,date], or [,]. This
- last option accesses all rows that ever existed.
-
- INSERTed rows get a timestamp too, so rows that were not in the table
- at the desired time will not appear.
-
- Vacuum removes rows that are no longer current. This time-warp feature
- is used by the engine for rollback and crash recovery. Expiration
- times can be set with purge.
-
- In 6.0, once a table is vacuumed, the creation time of a row may be
- incorrect, causing time-traval to fail.
-
- The time-travel feature will be removed in 7.0.
-
- 3.38) How do I tune the database engine for better performance?
-
- There are two things that can be done. You can use Openlink's option
- to disable fsync() by starting the postmaster with a '-o -F' option.
- This will prevent fsync()'s from flushing to disk after every
- transaction.
-
- You can also use the postmaster -B option to increase the number of
- shared memory buffers shared among the backend processes. If you make
- this parameter too high, the process will not start or crash
- unexpectedly. Each buffer is 8K and the defualt is 64 buffers.
-
- 3.39) What debugging features are available in PostgreSQL?
-
- PostgreSQL has several features that report status information that
- can be valuable for debugging purposes.
-
- First, by compiling with DEBUG defined, many assert()'s monitor the
- progress of the backend and halt the program when something unexpected
- occurs.
-
- Both postmaster and postgres have several debug options available.
- First, whenever you start the postmaster, make sure you send the
- standard output and error to a log file, like:
-
-
- cd /usr/local/pgsql
- ./bin/postmaster >server.log 2>&1 &
-
- This will put a server.log file in the top-level PostgreSQL directory.
- This file can contain useful information about problems or errors
- encountered by the server. Postmaster has a -d option that allows even
- more detailed information to be reported. The -d option takes a number
- 1-3 that specifies the debug level. The query plans in a verbose debug
- file can be formatted using the 'indent' program. (You may need to
- remove the '====' lines in 1.* releases.) Be warned that a debug level
- greater than one generates large log files in 1.* releases.
-
- You can actuall run the postgres backend from the command line, and
- type your SQL statement directly. This is recommended ONLY for
- debugging purposes. Note that a newline terminates the query, not a
- semicolon. If you have compiled with debugging symbols, you can
- perhaps use a debugger to see what is happening. Because the backend
- was not started from the postmaster, it is not running in an identical
- environment and locking/backend interaction problems may not be
- duplicated. Some operating system can attach to a running backend
- directly to diagnose problems.
-
- The postgres program has a -s, -A, -t options that can be very usefull
- for debugging and performance measurements.
-
- The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
- iterpreting your query.
-
- 3.40) What is an oid? What is a tid?
-
- Oids are Postgres's answer to unique row ids or serial columns. Every
- row that is created in Postgres gets a unique oid. All oids generated
- by initdb are less than 16384 (from backend/access/transam.h). All
- post-initdb (user-created) oids are equal or greater that this. All
- these oids are unique not only within a table, or database, but unique
- within the entire postgres installation.
-
- Postgres uses oids in its internal system tables to link rows in
- separate tables. These oids can be used to identify specific user rows
- and used in joins. It is recommended you use column type oid to store
- oid values. See the sql(l) manual page to see the other internal
- columns.
-
- Tids are used to indentify specific physical rows with block and
- offset values. Tids change after rows are modified or reloaded. They
- are used by index entries to point to physical rows. They can not be
- accessed through sql.
-
- 3.41) What is the meaning of some of the terms used in Postgres?
-
- Some of the source code and older documentation use terms that have
- more common usage. Here are some:
- * row, record, tuple
- * attribute, field, column
- * table, class
- * retrieve, select
- * replace, update
- * append, insert
- * oid, serial value
- * portal, cursor
- * range variable, table name, table alias
-
- Please let me know if you think of any more.
-
- 3.42) What is Genetic Query Optimization?
-
- The GEQO module in PostgreSQL is intended to solve the query
- optimization problem of joining many tables by means of a Genetic
- Algorithm (GA). It allows the handling of large join queries through
- non-exhaustive search.
-
- For further information see README.GEQO .
-
- 3.43) I am running Solaris and my dates display wrong. Why?
-
- Gcc under Solaris has an bug when compiled with optimization level 2.
- Edit 'configure', and change -O2 to -O, and recompile. If 'configure'
- does not exist in your top level source directory, make the change to
- Makefile.global.
-
- _________________________________________________________________
-
-Section 4: Extending PostgreSQL
-
- 4.1) I wrote a user-defined function and when I run it in psql, it dumps
- core.
-
- The problem could be a number of things. Try testing your user-defined
- function in a stand alone test program first. Also, make sure you are
- not sending elog NOTICES when the front-end is expecting data, such as
- during a type_in() or type_out() functions
-
- 4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not
- in alloc set!
-
- You are pfree'ing something that was not palloc'ed. When writing
- user-defined functions, do not include the file "libpq-fe.h". Doing so
- will cause your palloc to be a malloc instead of a free. Then, when
- the backend pfrees the storage, you get the notice message.
-
- 4.3) I've written some nifty new types and functions for PostgreSQL.
-
- Please share them with other PostgreSQL users. Send your extensions to
- mailing list, and they will eventually end up in the contrib/
- subdirectory.
-
- 4.4) How do I write a C function to return a tuple?
-
- This requires extreme wizardry, so extreme that the authors have not
- ever tried it, though in principle it can be done. The short answer is
- ... you can't. This capability is forthcoming in the future.
-
- _________________________________________________________________
-
-Section 5: Bugs
-
- 5.1) How do I make a bug report?
-
- Check the current FAQ at http://postgreSQL.org
-
- Also check out our ftp site ftp://ftp.postgreSQL.org/pub to see if
- there is a more recent PostgreSQL version.
-
- You can also fill out the "bug-template" file and send it to:
-
- This is the address of the developers mailing list.
+In 6.0, you can not directly create a multi-column index using create
+index. You need to define a function which acts on the multiple columns,
+then use create index with that function.
+In 6.1, this feature is available.
+
3.25) What are the temp_XXX files in my database
+directory?
+They are temp_ files generated by the query executor. For example, if a
+sort needs to be done to satisfy an ORDER BY, some temp files are
+generated as a result of the sort.
+If you have no transactions or sorts running at the time, it is safe to
+delete the temp_ files.
+
3.26) Why are my table files not getting any
+smaller after a delete?
+If you run vacuum in pre-6.0, unused rows will be marked for reuse, but
+the file blocks are not released.
+In 6.0, vacuum properly shrinks tables.
+
3.27) Why can't I connect to my database from
+another machine?
+The default configuration allows only connections from tcp/ip host
+localhost. You need to add a host entry to the file pgsql/data/pg_hba.
+
3.28) I get the error 'default index class
+unsupported' when creating an index. How do I do it?
+You probably used:
+
+ create index idx1 on person using btree (name);
+
+
+PostgreSQL indexes are extensible, and therefore in pre-6.0, you must
+specify a class_type when creating an index. Read the manual page for
+create index (called create_index).
+Version 6.0, if you do not specify a class_type, it defaults to the
+proper type for the column.
+
3.29) Why does creating an index crash the
+backend server?
+You have probably defined an incorrect *_ops type class for the field
+you are indexing.
+
3.30) How do I find out what indexes or
+operations are defined in the database?
+Run the file pgsql/src/tutorial/syscat.source. It illustrates many of
+the 'select's needed to get information out of the database system
+tables.
+
3.31) Why do statements require an extra character at
+the end? Why does 'createuser' return 'unexpected last match in input()'?
+Why does pg_dump fail?
+You have compile postgres with flex version 2.5.3. There is bug in this
+version of flex. Use flex version 2.5.2 or flex 2.5.4 instead. There
+is a doc/README.flex file which will properly patch the flex 2.5.3
+source code.
+
3.32) All my servers crash under concurrent table
+access. Why?
+This problem can be caused by a kernel that is not configured to support
+semaphores.
+
3.33) What tools are available for hooking
+postgres to Web pages?
+For web integration, PHP/FI is an excellent interface. The URL for that
+is
http://www.vex.net/php/+PHP is great for simple stuff, but for more complex stuff, some still
+use the perl interface and CGI.pm.
+An example of using WWW with C to talk to Postgres is can be tried at:
+
+
http://postgreSQL.org/~mlc+
+An WWW gatway based on WDB using perl can be downloaded from:
+
+
+href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb
+-p95
+
+
3.34) What is the time-warp feature and how does
+it relate to vacuum?
+PostgreSQL handles data changes differently than most database systems.
+When a row is changed in a table, the original row is marked with the
+time it was changed, and a new row is created with the current data. By
+default, only current rows are used in a table. If you specify a
+date/time after the table name in a FROM clause, you can access the data
+that was current at that time, i.e.
+
+ SELECT *
+ FROM employees ['July 24, 1996 09:00:00']
+
+
+displays employee rows in the table at the specified time. You can
+specify intervals like [date,date], [date,], [,date], or [,]. This last
+option accesses all rows that ever existed.
+INSERTed rows get a timestamp too, so rows that were not in the table at
+the desired time will not appear.
+Vacuum removes rows that are no longer current. This time-warp feature
+is used by the engine for rollback and crash recovery. Expiration times
+can be set with purge.
+In 6.0, once a table is vacuumed, the creation time of a row may be
+incorrect, causing time-traval to fail.
+The time-travel feature will be removed in 7.0.
+
3.35) How do I tune the database engine for
+better performance?
+There are two things that can be done. You can use Openlink's option to
+disable fsync() by starting the postmaster with a '-o -F' option. This
+will prevent fsync()'s from flushing to disk after every transaction.
+You can also use the postmaster -B option to increase the number of
+shared memory buffers shared among the backend processes. If you make
+this parameter too high, the process will not start or crash
+unexpectedly. Each buffer is 8K and the defualt is 64 buffers.
+
3.36) What debugging features are available in
+PostgreSQL?
+PostgreSQL has several features that report status information that can
+be valuable for debugging purposes.
+First, by compiling with DEBUG defined, many assert()'s monitor the
+progress of the backend and halt the program when something unexpected
+occurs.
+Both postmaster and postgres have several debug options available.
+First, whenever you start the postmaster, make sure you send the
+standard output and error to a log file, like:
+
+ cd /usr/local/pgsql
+ ./bin/postmaster >server.log 2>&1 &
+
+
+This will put a server.log file in the top-level PostgreSQL directory.
+This file can contain useful information about problems or errors
+encountered by the server. Postmaster has a -d option that allows even
+more detailed information to be reported. The -d option takes a number
+1-3 that specifies the debug level. The query plans in a verbose debug
+file can be formatted using the 'indent' program. (You may need to
+remove the '====' lines in 1.* releases.) Be warned that a debug level
+greater than one generates large log files in 1.* releases.
+You can actuall run the postgres backend from the command line, and type
+your SQL statement directly. This is recommended ONLY for debugging
+purposes. Note that a newline terminates the query, not a semicolon. If
+you have compiled with debugging symbols, you can perhaps use a debugger
+to see what is happening. Because the backend was not started from the
+postmaster, it is not running in an identical environment and
+locking/backend interaction problems may not be duplicated. Some
+operating system can attach to a running backend directly to diagnose
+problems.
+The postgres program has a -s, -A, -t options that can be very usefull
+for debugging and performance measurements.
+The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
+iterpreting your query.
+
3.37) What is an oid? What is a tid?
+Oids are Postgres's answer to unique row ids or serial columns. Every
+row that is created in Postgres gets a unique oid. All oids generated
+by initdb are less than 16384 (from backend/access/transam.h). All
+post-initdb (user-created) oids are equal or greater that this. All
+these oids are unique not only within a table, or database, but unique
+within the entire postgres installation.
+Postgres uses oids in its internal system tables to link rows in
+separate tables. These oids can be used to identify specific user rows
+and used in joins. It is recommended you use column type oid to store
+oid values. See the sql(l) manual page to see the other internal
+columns.
+Tids are used to indentify specific physical rows with block and offset
+values. Tids change after rows are modified or reloaded. They are used
+by index entries to point to physical rows. They can not be accessed
+through sql.
+
3.38) What is the meaning of some of the terms
+used in Postgres?
+Some of the source code and older documentation use terms that have more
+common usage. Here are some:
+
row, record, tuple
+
attribute, field, column
+
table, class
+
retrieve, select
+
replace, update
+
append, insert
+
oid, serial value
+
portal, cursor
+
range variable, table name, table alias
+
+Please let me know if you think of any more.
+
3.39) What is Genetic Query Optimization?
+The GEQO module in PostgreSQL is intended to solve the query
+optimization problem of joining many tables by means of a Genetic
+Algorithm (GA). It allows the handling of large join queries through
+non-exhaustive search.
+
3.40) I am running Solaris and my dates
+display wrong. Why?
+There was a bug in 6.0 that caused this problem under Solaris with -O2
+optimization.
+Upgrade to 6.1.
+
3.41) How do I enable more than 32 concurrent
+backends?
+Edit include/storage/sinvaladt.h, and change the value of MaxBackendId.
+In the future, we plan to make this a configurable prameter.
+
+
Section 4: Extending PostgreSQL
+
+
4.1) I wrote a user-defined function and when I run it
+in psql, it dumps core.
+The problem could be a number of things. Try testing your user-defined
+function in a stand alone test program first. Also, make sure you are
+not sending elog NOTICES when the front-end is expecting data, such as
+during a type_in() or type_out() functions
+
4.2) I get messages of the type
+ NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!
+You are pfree'ing something that was not palloc'ed. When writing
+user-defined functions, do not include the file "libpq-fe.h". Doing so
+will cause your palloc to be a malloc instead of a free. Then, when the
+backend pfrees the storage, you get the notice message.
+
4.3) I've written some nifty new types and functions for
+PostgreSQL.
+Please share them with other PostgreSQL users. Send your extensions to
+mailing list, and they will eventually end up in the contrib/
+subdirectory.
+
4.4) How do I write a C function to return a tuple?
+This requires extreme wizardry, so extreme that the authors have not
+ever tried it, though in principle it can be done. The short answer is
+... you can't. This capability is forthcoming in the future.
+
+
Section 5: Bugs
+
+
5.1) How do I make a bug report?
+Check the current FAQ at
+href="http://postgreSQL.org">http://postgreSQL.org
+Also check out our ftp site
+href="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub to
+see if there is a more recent PostgreSQL version.
+You can also fill out the "bug-template" file and send it to:
+
+This is the address of the developers mailing list.
+
+
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