-
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?
+ 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 or 4.x
+ * 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 6.1.1, which will be
+ released in July, 1997. For information about what is new in 6.1.1,
+ 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.
+
+ Upgrading to 6.1 requires a dump and restore from previous releases.
+
+ Upgrading from 6.1 to 6.1.1 requires a compile of the new release,
+ recompile of all your custom applications to use the new libpq, and
+ then an install while the postmaster is temporarily stopped.
+
+ 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 6.1.1.
+
+ 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
+
+ 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) 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
+
+ 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?
+
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?
-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.
-
-
projects / postgresql.git / commitdiff