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@ -5,8 +5,8 @@
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
The most recent version of this document can be viewed at the
PostgreSQL Web site, http://www.PostgreSQL.org.
The most recent version of this document can be viewed at
http://www.PostgreSQL.org/docs/faq-english.html.
Linux-specific questions are answered in
http://www.PostgreSQL.org/docs/faq-linux.html.
@ -28,9 +28,9 @@
1.3) What Unix platforms does PostgreSQL run on?
1.4) What non-unix ports are available?
1.5) Where can I get PostgreSQL?
1.6) Where can I get support for PostgreSQL?
1.7) What is the latest release of PostgreSQL?
1.8) What documentation is available for PostgreSQL?
1.6) Where can I get support?
1.7) What is the latest release?
1.8) What documentation is available?
1.9) How do I find out about known bugs or missing features?
1.10) How can I learn SQL?
1.11) Is PostgreSQL Y2K compliant?
@ -53,8 +53,8 @@
/usr/local/pgsql?
3.3) When I start the postmaster, I get a Bad System Call or core
dumped message. Why?
3.4) When I try to start the postmaster, I get IpcMemoryCreate
errors3. Why?
3.4) When I try to start the postmaster, I get IpcMemoryCreate errors.
Why?
3.5) When I try to start the postmaster, I get IpcSemaphoreCreate
errors. Why?
3.6) How do I prevent other hosts from accessing my PostgreSQL
@ -63,22 +63,22 @@
3.8) Why can't I access the database as the root user?
3.9) All my servers crash under concurrent table access. Why?
3.10) How do I tune the database engine for better performance?
3.11) What debugging features are available in PostgreSQL?
3.12) I get 'Sorry, too many clients' when trying to connect. Why?
3.13) What are the pg_psort.XXX files in my database directory?
3.11) What debugging features are available?
3.12) I get "Sorry, too many clients" when trying to connect. Why?
3.13) What are the pg_sorttempNNN.NN files in my database directory?
Operational Questions
4.1) The system seems to be confused about commas, decimal points, and
date formats.
4.1) Why is the system confused about commas, decimal points, and date
formats.
4.2) What is the exact difference between binary cursors and normal
cursors?
4.3) How do I select only the first few rows of a query?
4.4) How do I get a list of tables, or other things I can see in psql?
4.3) How do I SELECT only the first few rows of a query?
4.4) How do I get a list of tables or other things I can see in psql?
4.5) How do you remove a column from a table?
4.6) What is the maximum size for a row, table, database?
4.7) How much database disk space is required to store data from a
typical flat file?
typical text file?
4.8) How do I find out what indices or operations are defined in the
database?
4.9) My queries are slow or don't make use of the indexes. Why?
@ -86,7 +86,7 @@
4.11) What is an R-tree index?
4.12) What is Genetic Query Optimization?
4.13) How do I do regular expression searches and case-insensitive
regexp searching?
regular expression searching?
4.14) In a query, how do I detect if a field is NULL?
4.15) What is the difference between the various character types?
4.16.1) How do I create a serial/auto-incrementing field?
@ -110,7 +110,7 @@
it dump core?
5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0
not in alloc set! mean?
5.3) How can I contribute some nifty new types and functions for
5.3) How can I contribute some nifty new types and functions to
PostgreSQL?
5.4) How do I write a C function to return a tuple?
5.5) I have changed a source file. Why does the recompile does not see
@ -131,7 +131,7 @@
developers who all subscribe to the PostgreSQL development mailing
list. The current coordinator is Marc G. Fournier
(scrappy@PostgreSQL.org). (See below on how to join). This team is now
responsible for all current and future development of PostgreSQL.
responsible for all 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
@ -205,14 +205,14 @@
libpq library and psql.
The database server is now working on Windows NT using the Cygnus
Unix/NT porting library. See pgsql/doc/README.NT in the distribution.
Unix/NT porting library. See pgsql/doc/FAQ_NT in the distribution.
1.5) Where can I get PostgreSQL?
The primary anonymous ftp site for PostgreSQL is
ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main web site.
1.6) Where can I get support for PostgreSQL?
1.6) Where can I get support?
There is no official support for PostgreSQL from the University of
California, Berkeley. It is maintained through volunteer effort.
@ -258,26 +258,25 @@
Commercial support for PostgreSQL is available at
http://www.pgsql.com/.
1.7) What is the latest release of PostgreSQL?
1.7) What is the latest release?
The latest release of PostgreSQL is version 7.0.2.
We plan to have major releases every four months.
1.8) What documentation is available for PostgreSQL?
1.8) What documentation is available?
Several manuals, manual pages, and some small test examples are
included in the distribution. See the /doc directory. You can also
browse the manual on-line at http://www.PostgreSQL.org/docs/postgres.
in the distribution.
There is a PostgreSQL book availiable at
http://www.PostgreSQL.org/docs/awbook.html
There is a PostgreSQL book available at
http://www.PostgreSQL.org/docs/awbook.html.
psql has some nice \d commands to show information about types,
operators, functions, aggregates, etc.
The web site contains even more documentation.
Our web site contains even more documentation.
1.9) How do I find out about known bugs or missing features?
@ -310,10 +309,10 @@
submit high-quality patches to pgsql-patches.
There are about a dozen people who have commit privileges to the
PostgreSQL CVS archive. All of them have submitted so many
high-quality patches that it was a pain for the existing committers to
keep up, and we had confidence that patches they committed were likely
to be of high quality.
PostgreSQL CVS archive. They each have submitted so many high-quality
patches that it was a pain for the existing committers to keep up, and
we had confidence that patches they committed were likely to be of
high quality.
1.13) How do I submit a bug report?
@ -347,8 +346,7 @@
though in this mode, an OS crash could cause data corruption.
We are working to provide an intermediate mode that suffers
less performance overhead than full fsync mode, and will allow
data integrity within 30 seconds of an OS crash. The mode is
select-able by the database administrator.
data integrity within 30 seconds of an OS crash.
In comparison to MySQL or leaner database systems, we are
slower on inserts/updates because we have transaction overhead.
Of course, MySQL doesn't have any of the features mentioned in
@ -393,7 +391,7 @@
There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.
PsqlODBC is included in the distribution. More information about it
can be gotten from: ftp://ftp.PostgreSQL.org/pub/odbc/index.html
can be gotten from ftp://ftp.PostgreSQL.org/pub/odbc/.
OpenLink ODBC can be gotten from http://www.openlinksw.com. It works
with their standard ODBC client software so you'll have PostgreSQL
@ -413,7 +411,7 @@
There is also one at http://www.phone.net/home/mwm/hotlist/.
For web integration, PHP is an excellent interface. It is at:
For web integration, PHP is an excellent interface. It is at
http://www.php.net
PHP is great for simple stuff, but for more complex cases, many use
@ -473,12 +471,12 @@
3.4) When I try to start the postmaster, I get IpcMemoryCreate errors. Why?
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 and backend processes you configure postmaster to run with.
For most systems, with default numbers of buffers and processes, you
need a minimum of ~1MB.
You either do not have shared memory configured properly in your
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 and backend processes you configure postmaster to run
with. For most systems, with default numbers of buffers and processes,
you need a minimum of ~1MB.
3.5) When I try to start the postmaster, I get IpcSemaphoreCreate errors.
Why?
@ -507,8 +505,7 @@
The default configuration allows only unix domain socket connections
from the local machine. To enable TCP/IP connections, make sure the
postmaster has been started with the -i option, and add an appropriate
host entry to the file pgsql/data/pg_hba.conf. See the pg_hba.conf
manual page.
host entry to the file pgsql/data/pg_hba.conf.
3.8) Why can't I access the database as the root user?
@ -529,11 +526,11 @@
indices are being used.
If you are doing a lot of INSERTs, consider doing them in a large
batch using the COPY command. This is much faster than single
individual INSERTS. Second, statements not in a BEGIN WORK/COMMIT
transaction block are considered to be in their own transaction.
Consider performing several statements in a single transaction block.
This reduces the transaction overhead. Also consider dropping and
batch using the COPY command. This is much faster than individual
INSERTS. Second, statements not in a BEGIN WORK/COMMIT transaction
block are considered to be in their own transaction. Consider
performing several statements in a single transaction block. This
reduces the transaction overhead. Also consider dropping and
recreating indices when making large data changes.
There are several tuning things that can be done. You can disable
@ -542,7 +539,7 @@
You can also use the postmaster -B option to increase the number of
shared memory buffers used by the backend processes. If you make this
parameter too high, the postmaster may not start up because you've
parameter too high, the postmaster may not start because you've
exceeded your kernel's limit on shared memory space. Each buffer is 8K
and the default is 64 buffers.
@ -550,10 +547,10 @@
of memory used by the backend process for temporary sorts. The -S
value is measured in kilobytes, and the default is 512 (ie, 512K).
You can also use the CLUSTER command to group data in base tables to
match an index. See the cluster(l) manual page for more details.
You can also use the CLUSTER command to group data in tables to match
an index. See the cluster(l) manual page for more details.
3.11) What debugging features are available in PostgreSQL?
3.11) What debugging features are available?
PostgreSQL has several features that report status information that
can be valuable for debugging purposes.
@ -607,7 +604,7 @@
In PostgreSQL 6.5 and up, the default limit is 32 processes. You can
increase it by restarting the postmaster with a suitable -N value.
With the default configuration you can set -N as large as 1024; if you
With the default configuration you can set -N as large as 1024. If you
need more, increase MAXBACKENDS in include/config.h and rebuild. You
can set the default value of -N at configuration time, if you like,
using configure's --with-maxbackends switch.
@ -622,33 +619,32 @@
processes, NPROC, the maximum number of processes per user, MAXUPRC,
and the maximum number of open files, NFILE and NINODE. The reason
that PostgreSQL has a limit on the number of allowed backend processes
is so that you can ensure that your system won't run out of resources.
is so your system won't run out of resources.
In PostgreSQL versions prior to 6.5, the maximum number of backends
was 64, and changing it required a rebuild after altering the
MaxBackendId constant in include/storage/sinvaladt.h.
3.13) What are the pg_tempNNN.NN files in my database directory?
3.13) What are the pg_sorttempNNN.NN files in my database directory?
They are temporary files generated by the query executor. For example,
if a sort needs to be done to satisfy an ORDER BY, and the sort
requires more space than the backend's -S parameter allows, then temp
files are created to hold the extra data.
The temp files should go away automatically, but might not if a
backend crashes during a sort. If you have no transactions running at
the time, it is safe to delete the pg_tempNNN.NN files.
The temp files should be deleted automatically, but might not if a
backend crashes during a sort. If you have no backends running at the
time, it is safe to delete the pg_tempNNN.NN files.
_________________________________________________________________
Operational Questions
4.1) The system seems to be confused about commas, decimal points, and date
formats.
4.1) Why is system 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. There are postgres and
psql SET commands to control the date format. Set those accordingly
for your operating environment.
Check your locale configuration. PostgreSQL uses the locale setting of
the user that ran the postmaster process. There are postgres and psql
SET commands to control the date format. Set those accordingly for
your operating environment.
4.2) What is the exact difference between binary cursors and normal
cursors?
@ -665,12 +661,13 @@
only the first few records requested, or the entire query may have to
be evaluated until the desired rows have been generated.
4.4) How do I get a list of tables, or other information I see in psql?
4.4) How do I get a list of tables or other things I can see in psql?
You can read the source code for psql, file pgsql/src/bin/psql/psql.c.
It contains SQL commands that generate the output for psql's backslash
commands. You can also start psql with the -E option so that it will
print out the queries it uses to execute the commands you give.
You can read the source code for psql in file
pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the
output for psql's backslash commands. You can also start psql with the
-E option so it will print out the queries it uses to execute the
commands you give.
4.5) How do you remove a column from a table?
@ -701,10 +698,10 @@ Maximum number of indexes on a table? unlimited
Row length limit will be removed in 7.1.
4.7)How much database disk space is required to store data from a typical
flat file?
text file?
A PostgreSQL database can require about six and a half times the disk
space required to store the data in a flat file.
A PostgreSQL database may need six and a half times the disk space
required to store the data in a flat file.
Consider a file of 300,000 lines with two integers on each line. The
flat file is 2.4MB. The size of the PostgreSQL database file
@ -727,7 +724,7 @@ Maximum number of indexes on a table? unlimited
1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB)
Indexes do not contain as much overhead, but do contain the data that
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
4.8) How do I find out what indices or operations are defined in the
@ -742,12 +739,12 @@ Maximum number of indexes on a table? unlimited
4.9) My queries are slow or don't make use of the indexes. 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 knows how many rows in the table, and can
better decide if it should use indices. Note that the optimizer does
not use indices in cases when the table is small because a sequential
scan would be faster.
PostgreSQL does not automatically maintain statistics. VACUUM must be
run to update the statistics. After statistics are updated, the
optimizer knows how many rows in the table, and can better decide if
it should use indices. Note that the optimizer does not use indices in
cases when the table is small because a sequential scan would be
faster.
For column-specific optimization statistics, use VACUUM ANALYZE.
VACUUM ANALYZE is important for complex multi-join queries, so the
@ -794,15 +791,12 @@ Maximum number of indexes on a table? unlimited
4.12) 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.
The GEQO module speeds query optimization when 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 the documentation.
4.13) How do I do regular expression searches and case-insensitive regexp
searching?
4.13) How do I do regular expression searches and case-insensitive regular
expression searching?
The ~ operator does regular-expression matching, and ~* does
case-insensitive regular-expression matching. There is no
@ -837,7 +831,7 @@ BYTEA bytea variable-length array of bytes
4.16.1) How do I create a serial/auto-incrementing field?
PostgreSQL supports SERIAL data type. It auto-creates a sequence and
PostgreSQL supports a SERIAL data type. It auto-creates a sequence and
index on the column. For example, this:
CREATE TABLE person (
id SERIAL,
@ -861,10 +855,10 @@ BYTEA bytea variable-length array of bytes
4.16.2) How do I get the back the generated SERIAL value after an insert?
Probably the simplest approach is to to retrieve the next SERIAL value
from the sequence object with the nextval() function before inserting
and then insert it explicitly. Using the example table in 4.16.1, that
might look like this:
One approach is to to retrieve the next SERIAL value from the sequence
object with the nextval() function before inserting and then insert it
explicitly. Using the example table in 4.16.1, that might look like
this:
$newSerialID = nextval('person_id_seq');
INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
@ -874,8 +868,8 @@ BYTEA bytea variable-length array of bytes
named <table>_<serialcolumn>_seq, where table and serialcolumn are the
names of your table and your SERIAL column, respectively.
Similarly, you could retrieve the just-assigned SERIAL value with the
currval() function after it was inserted by default, e.g.,
Alternatively, you could retrieve the just-assigned SERIAL value with
the currval() function after it was inserted by default, e.g.,
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
@ -888,11 +882,11 @@ BYTEA bytea variable-length array of bytes
4.16.3) Don't currval() and nextval() lead to a race condition with other
concurrent backend processes?
No. That has been handled by the backends.
No. This is handled by the backends.
4.17) What is an oid? What is a tid?
Oids are PostgreSQL's answer to unique row ids. Every row that is
OIDs are PostgreSQL's answer to unique row ids. Every row that is
created in PostgreSQL gets a unique oid. All oids generated during
initdb are less than 16384 (from backend/access/transam.h). All
user-created oids are equal or greater that this. By default, all
@ -902,15 +896,15 @@ BYTEA bytea variable-length array of bytes
PostgreSQL uses oids in its internal system tables to link rows
between 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.
oid values. You can create an index on the oid field for faster
access.
Oids are assigned to all new rows from a central area that is used by
all databases. If you want to change the oid to something else, or if
you want to make a copy of the table, with the original oid's, there
is no reason you can't do it:
CREATE TABLE new_table(old_oid oid, mycol int);
SELECT INTO new SELECT old_oid, mycol FROM old;
SELECT old_oid, mycol INTO new FROM old;
COPY new TO '/tmp/pgtable';
DELETE FROM new;
COPY new WITH OIDS FROM '/tmp/pgtable';
@ -957,12 +951,11 @@ BYTEA bytea variable-length array of bytes
You need to put BEGIN WORK and COMMIT around any use of a large object
handle, that is, surrounding lo_open ... lo_close.
Current PostgreSQL enforces the rule by closing large object handles
at transaction commit, which will be instantly upon completion of the
lo_open command if you are not inside a transaction. So the first
attempt to do anything with the handle will draw invalid large obj
descriptor. So code that used to work (at least most of the time) will
now generate that error message if you fail to use a transaction.
Currently PostgreSQL enforces the rule by closing large object handles
at transaction commit. So the first attempt to do anything with the
handle will draw invalid large obj descriptor. So code that used to
work (at least most of the time) will now generate that error message
if you fail to use a transaction.
If you are using a client interface like ODBC you may need to set
auto-commit off.
@ -1018,8 +1011,7 @@ BYTEA bytea variable-length array of bytes
You are pfree'ing something that was not palloc'ed. Beware of mixing
malloc/free and palloc/pfree.
5.3) How can I contribute some nifty new types and functions for
PostgreSQL?
5.3) How can I contribute some nifty new types and functions to PostgreSQL?
Send your extensions to the pgsql-hackers mailing list, and they will
eventually end up in the contrib/ subdirectory.