+href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wd
+b
+-p95
+
+
1.13) Does PostgreSQL have a graphical user interface
+?
+A report generator? A embedded query language interface?
+We have a nice graphical user interface called pgaccess, which is
+shipped as part of the distribtion. Pgaccess also has a report
+generator.
+We also have ecpg, which is an embedded SQL query language interface for
+C. This is also included.
+
1.14) What is a good book to learn SQL?
+Many of our users like The Practical SQL Handbook,
+Bowman et al, Addison Wesley.
+
+
+
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 tha
+n
+/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.
-
+
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?
-
+
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'.
-
-2.8) How do I prevent other hosts from accessing my PostgreSQL backend?
-
-Use host-based authentication by modifying the file $PGDATA/pg_hba
+
2.8) How do I prevent other hosts from accessing my
+PostgreSQL backend?
+By default, PostgreSQL only allows connections from the local machine
+using unix domain. You must add the -i flag to the postmaster, and
+enable host-based authentication by modifying the file $PGDATA/pg_hba
accordingly.
-
-2.9) 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.
-
-2.10) All my servers crash under concurrent table access. Why?
-
+
2.9) 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.
+
2.10) All my servers crash under concurrent table
+access. Why?
This problem can be caused by a kernel that is not configured to support
semaphores.
-
-2.11) 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.
-
-You can also use the postgres -S option to increase the maximum amount of
-memory used by each backend process for temporary sorts. Each buffer is 1K
-and the defualt is 512 buffers.
-
-2.12) What debugging features are available in PostgreSQL?
-
-PostgreSQL has several features that report status information that can be
-valuable for debugging purposes.
-
-First, by running configure with the -enable-cassert option, 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:
-
+
2.11) How do I tune the database engine for
+better performance?
+There are two things that can be done. You can 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.
+You can also use the postgres -S option to increase the maximum
+amount of memory used by each backend process for temporary sorts.
+Each buffer is 1K and the defualt is 512 buffers.
+
2.12) What debugging features are available in
+PostgreSQL?
+PostgreSQL has several features that report status information that can
+be valuable for debugging purposes.
+First, by running configure with the -enable-cassert option,
+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. Be warned that a debug level of 3 generates large log
-files.
-
+ ./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. Be warned that a debug level
+of 3 generates large log files.
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 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.
-
+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 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.
You can also compile with profiling to see what functions are taking
-execution time. The backend profile files will be deposited in the
-pgsql/data/base/dbname directory. The client profile file will be put in the
-current directory.
-
+execution time. The backend profile files will be deposited in the
+pgsql/data/base/dbname directory. The client profile file will be put
+in the current directory.
The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
interpreting your query.
-
-2.13) 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 3: PostgreSQL Features
-
-3.1) Does PostgreSQL support nested subqueries?
-
-Subqueries are not implemented, but they can be simulated using sql
-functions.
-
-3.2) 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.
-
-3.3) 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.
-
-3.4) How can I write client applications to PostgreSQL?
-
-PostgreSQL supports a C-callable library interface called libpq as well as
-many others. See the /src/interfaces directory.
-
-Others have contributed a perl interface and a WWW gateway to PostgreSQL.
-See the PostgreSQL home pages for more details.
-
-3.5) How do I set up a pg_group?
-
+
2.13) 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 3: PostgreSQL Features
+
+
3.1) Does PostgreSQL support nested subqueries?
+Yes.
+
3.2) I've having a lot of problems using rules.
+Currently, the rule system in PostgreSQL has some limitations. It works
+enough to support the view mechanism, but does not handle
+Insert/Update/Delete well.
+
3.3) I can't seem to write into the middle of large
+objects reliably.
+The Inversion large object system now works perfectly. You should no
+longer have problems with large objects.
+
3.4) How can I write client applications to PostgreS
+QL?
+PostgreSQL supports a C-callable library interface called libpq as well
+as many others. See the /src/interfaces directory.
+Others have contributed a perl interface and a WWW gateway to
+PostgreSQL. See the PostgreSQL home pages for more details.
+
3.5) 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}');
+
+ jolly=> insert into pg_group (groname, grosysid, grolist)
+ jolly=> values ('posthackers', '1234', '{5443, 8261}');
INSERT 548224
- jolly=> grant insert on foo to group posthackers;
+ 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[].
-
-3.6) What is the exact difference between binary cursors and normal cursors?
-
-See the declare manual page for a description.
-
-3.7) 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.
-
+ 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[].
+
+
3.6) What is the exact difference between binary
+cursors and normal cursors?
+See the declare manual page for a description.
+
3.7) 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"
-
-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.
-
-3.8) 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.
-
-3.9) 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). For column-specific optimization statistics, use 'vacuum
-analyze'.
-
-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.
-
+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"
+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.
+
3.8) 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.
+
3.9) 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). For column-specific optimization
+statistics, use 'vacuum analyze'.
+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.
-
-3.10) How do I do regular expression searches? case-insensitive regexp
-searching?
-
-See the pgbuiltin manual page. Search for regular expression.
-
-3.11) I experienced a server crash during a vacuum. How do I remove the lock
-file?
-
-See the vacuum manual page.
-
-3.12) What is the difference between the various character types?
-
+
3.10) How do I do regular expression searches?
+case-insensitive regexp searching?
+See the pgbuiltin manual page. Search for regular expression.
+
3.11) I experienced a server crash during a
+vacuum. How do I remove the lock file?
+See the vacuum manual page.
+
3.12) 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
-
+
You need to use the internal name when doing internal operations.
-
-The last four types above are "varlena" types (i.e. the first four bytes are
-the length, followed by the data). CHAR(#) allocates the maximum number of
-bytes no matter how much data is stored in the field. TEXT, VARCHAR(#), and
-BYTEA all have variable length on the disk, and because of this, there is a
-small performance penalty for using them. Specifically, the penalty is for
-access to any columns after the first column of this type.
-
-3.13) In a query, how do I detect if a field is NULL?
-
+The last four types above are "varlena" types (i.e. the first four bytes
+are the length, followed by the data). CHAR(#) allocates the maximum
+number of bytes no matter how much data is stored in the field.
+TEXT, VARCHAR(#), and BYTEA all have variable length on the disk, and
+because of this, there is a small performance penalty for using them.
+Specifically, the penalty is for access to any columns after the first
+column of this type.
+
3.13) In a query, how do I detect if a field is NULL?
+
You test the column with IS NULL and IS NOT NULL.
-
-3.14) How do I see how the query optimizer is evaluating my query?
-
-See the explain manual page.
-
-3.15) 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 use pgdump's -o option or
-COPY's WITH OIDS option to preserver the oids.
-
-We also have a SEQUENCE function that is similar to SERIAL. See the
+
3.14) How do I see how the query optimizer is
+evaluating my query?
+See the explain manual page.
+
3.15) 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 use
+pgdump's -o option or COPY's WITH OIDS option to preserver the oids.
+We also have a SEQUENCE function that is similar to SERIAL. See the
create_sequence manual page.
-
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.
-
-Yet another way is to use general trigger function autoinc() from
-contrib/spi/autoinc.c.
-
-3.16) What are the pg_psort.XXX files in my database directory?
-
-They are temporary sort 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.
-
+
+
+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.
+Yet another way is to use general trigger function autoinc()
+from contrib/spi/autoinc.c.
+
3.16) What are the pg_psort.XXX files in my database
+directory?
+They are temporary sort 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 pg_psort.XXX files.
-
-3.17) 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. See
-the hba_conf manual page.
-
-3.18) 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.
-
-3.19) 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 6.3.
-
-3.20) 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. You can create an
-index on the oid field for faster access.
-
+
3.17) Why can't I connect to my database from
+another machine?
+The default configuration allows only unix domain socket connections
+from the local machine. To enable TCP/IP connections, use the
+postmaster -i option You need to add a host entry to the file
+pgsql/data/pg_hba. See the hba_conf manual page.
+
3.18) How do I find out what indexes or
+operations are defined in the database?
+psql has a variety of backslash commands to show such information. Use
+\? to see them.
+Also try the file pgsql/src/tutorial/syscat.source. It illustrates many of
+the 'select's needed to get information out of the database system
+tables.
+
3.19) What is the time-warp feature and how does
+it relate to vacuum?
+PostgreSQL no longer supports this feature. All support code has been
+removed. This was done to improve performance and reduce disk storage
+overhead.
+
3.20) 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. You can create an index on the oid field for faster access.
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.
-
-3.21) What is the meaning of some of the terms used in Postgres?
-
+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.
+
3.21) 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
-
+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.
-
-3.22) 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 .
-
-3.23) How do you remove a column from a table?
-
+
3.22) 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.
+
3.23) How do you remove a column from a table?
We do not support ALTER TABLE DROP COLUMN, but do this:
-
+
SELECT ... -- select all columns but the one you want to remove
INTO TABLE new_table
FROM old_table;
DROP TABLE old_table;
ALTER TABLE new_table RENAME TO old_table;
-
-3.24) How do SELECT only the first few rows of a query?
-
-See the fetch manual page.
-
-This only prevents all row results from being transfered to the client. The
-entire query must be evaluated, even if you only want just first few rows.
-Consider a query that has and ORDER BY. There is no way to return any rows
-until the entire query is evaluated and sorted.
-
-3.25) Why can't I create a column named "time"?
-
+
+
+
3.24) How do SELECT only the first few rows of
+a query?
+See the fetch manual page.
+This only prevents all row results from being transfered to the client.
+The entire query must be evaluated, even if you only want just first few
+rows.
+Consider a query that has and ORDER BY. There is no way to return any
+rows until the entire query is evaluated and sorted.
+
3.25) Why can't I create a column named
+"time"?
6.2.1 has added some new restricted keywords as we make PostgreSQL more
-ANSI-92 compilant. The next release will have this restriction removed.
+ANSI-92 compilant. The next release will have this restriction removed.
There is a patch on ftp.postgresql.org that will allow this feature now.
-
-3.26)How much database disk space is required to store data from a typical
-flat file?
-
-Consider a file with 300,000 lines with two integers on each line. The flat
-file is 2.4MB. The size of the PostgreSQL database file containing this data
-can be estimated:
-
+
3.26)How much database disk space is required
+to store data from a typical flat file?
+Consider a file with 300,000 lines with two integers on each line.
+The flat file is 2.4MB. The size of the PostgreSQL database file
+containing this data can be estimated:
40 bytes + each row header (approximate)
8 bytes + two int fields @ 4 bytes each
4 bytes + pointer on page to tuple
157 rows per page
1911 database pages * 8192 bytes per page = 15,654,912 or 15.5MB
-
Indexes do not contain as much overhead, but do contain the data that
is being indexed, so they can be large also.
-
- ------------------------------------------------------------------------
-
-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.
-
+
+
+
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?<
+/H3>
+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