|
|
|
|
@ -10,7 +10,7 @@ |
|
|
|
|
alink="#0000ff"> |
|
|
|
|
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> |
|
|
|
|
|
|
|
|
|
<P>Last updated: Sat Nov 27 00:14:59 EST 2004</P> |
|
|
|
|
<P>Last updated: Sat Nov 27 23:55:37 EST 2004</P> |
|
|
|
|
|
|
|
|
|
<P>Current maintainer: Bruce Momjian (<A href= |
|
|
|
|
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> |
|
|
|
|
@ -111,8 +111,8 @@ |
|
|
|
|
serial/auto-incrementing field?<BR> |
|
|
|
|
<A href="#4.15.2">4.15.2</A>) How do I get the value of a |
|
|
|
|
<SMALL>SERIAL</SMALL> insert?<BR> |
|
|
|
|
<A href="#4.15.3">4.15.3</A>) Don't <I>currval()</I> and |
|
|
|
|
<I>nextval()</I> lead to a race condition with other users?<BR> |
|
|
|
|
<A href="#4.15.3">4.15.3</A>) Doesn't <I>currval()</I> |
|
|
|
|
lead to a race condition with other users?<BR> |
|
|
|
|
<A href="#4.15.4">4.15.4</A>) Why aren't my sequence numbers |
|
|
|
|
reused on transaction abort? Why are there gaps in the numbering of |
|
|
|
|
my sequence/SERIAL column?<BR> |
|
|
|
|
@ -395,10 +395,9 @@ |
|
|
|
|
|
|
|
|
|
<H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4> |
|
|
|
|
|
|
|
|
|
<P>Please visit the PostgreSQL BugTool page at <A href= |
|
|
|
|
"http://www.PostgreSQL.org/bugs/bugs.php">http://www.PostgreSQL.org/bugs/bugs.php</A>, |
|
|
|
|
which gives guidelines and directions on how to submit a |
|
|
|
|
bug report.</P> |
|
|
|
|
<P>Visit the PostgreSQL bug form at <A href= |
|
|
|
|
"http://www.postgresql.org/bugform.html"> |
|
|
|
|
http://www.postgresql.org/bugform.html</A>.</P> |
|
|
|
|
|
|
|
|
|
<P>Also check out our ftp site <A href= |
|
|
|
|
"ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to |
|
|
|
|
@ -546,7 +545,9 @@ |
|
|
|
|
http://www.pgaccess.org</a>), PgAdmin III (<a |
|
|
|
|
href="http://www.pgadmin.org">http://www.pgadmin.org</a>, RHDB Admin (<a |
|
|
|
|
href="http://sources.redhat.com/rhdb/">http://sources.redhat.com/rhdb/ |
|
|
|
|
</a>) and Rekall (<a href="http://www.thekompany.com/products/rekall/"> |
|
|
|
|
</a>), TORA (<a href="http://www.globecom.net/tora/">http://www.globecom.net/tora/ |
|
|
|
|
(partly commercial)</a>, and Rekall |
|
|
|
|
(<a href="http://www.thekompany.com/products/rekall/"> |
|
|
|
|
http://www.thekompany.com/products/rekall/</a>, proprietary). There is |
|
|
|
|
also PhpPgAdmin (<a href="http://phppgadmin.sourceforge.net/"> |
|
|
|
|
http://phppgadmin.sourceforge.net/ </a>), a web-based interface to |
|
|
|
|
@ -606,10 +607,9 @@ |
|
|
|
|
how many buffers and backend processes you configure for |
|
|
|
|
<I>postmaster</I>. For most systems, with default numbers of |
|
|
|
|
buffers and processes, you need a minimum of ~1 MB. See the <A |
|
|
|
|
href= |
|
|
|
|
"http://www.PostgreSQL.org/docs/view.php?version=current&idoc=1&file=kernel-resources.html">PostgreSQL |
|
|
|
|
Administrator's Guide</A> for more detailed information about |
|
|
|
|
shared memory and semaphores.</P> |
|
|
|
|
href="http://www.postgresql.org/docs/current/static/kernel-resources.html">PostgreSQL |
|
|
|
|
Administrator's Guide/Server Run-time Environment/Managing Kernel Resources</A> |
|
|
|
|
section for more detailed information about shared memory and semaphores.</P> |
|
|
|
|
|
|
|
|
|
<H4><A name="3.4">3.4</A>) When I try to start <I>postmaster</I>, I |
|
|
|
|
get <I>IpcSemaphoreCreate</I> errors. Why?</H4> |
|
|
|
|
@ -645,8 +645,9 @@ |
|
|
|
|
better performance?</H4> |
|
|
|
|
|
|
|
|
|
<P>Certainly, indexes can speed up queries. The |
|
|
|
|
<SMALL>EXPLAIN ANALYZE</SMALL> command allows you to see how PostgreSQL is |
|
|
|
|
interpreting your query, and which indexes are being used.</P> |
|
|
|
|
<SMALL>EXPLAIN ANALYZE</SMALL> command allows you to see how |
|
|
|
|
PostgreSQL is interpreting your query, and which indexes are |
|
|
|
|
being used.</P> |
|
|
|
|
|
|
|
|
|
<P>If you are doing many <SMALL>INSERTs</SMALL>, consider doing |
|
|
|
|
them in a large batch using the <SMALL>COPY</SMALL> command. This |
|
|
|
|
@ -657,22 +658,23 @@ |
|
|
|
|
reduces the transaction overhead. Also, consider dropping and |
|
|
|
|
recreating indexes when making large data changes.</P> |
|
|
|
|
|
|
|
|
|
<P>There are several tuning options. You can disable <I>fsync()</I> |
|
|
|
|
by starting <I>postmaster</I> with a <I>-o -F</I> option. This will |
|
|
|
|
<P>There are several tuning options in the <a href= |
|
|
|
|
"http://www.postgresql.org/docs/current/static/runtime.html"> |
|
|
|
|
Administration Guide/Server Run-time Environment/Run-time Configuration</a>. |
|
|
|
|
You can disable <I>fsync()</I> by using <i>fsync</I> option. This will |
|
|
|
|
prevent <I>fsync()</I>s from flushing to disk after every |
|
|
|
|
transaction.</P> |
|
|
|
|
|
|
|
|
|
<P>You can also use the <I>postmaster</I> <I>-B</I> option to |
|
|
|
|
<P>You can use the <I>shared_buffers</I> option to |
|
|
|
|
increase the number of shared memory buffers used by the backend |
|
|
|
|
processes. If you make this parameter too high, the |
|
|
|
|
<I>postmaster</I> may not start because you have exceeded your |
|
|
|
|
kernel's limit on shared memory space. Each buffer is 8K and the |
|
|
|
|
default is 64 buffers.</P> |
|
|
|
|
default is 1000 buffers.</P> |
|
|
|
|
|
|
|
|
|
<P>You can also use the backend <I>-S</I> option to increase the |
|
|
|
|
maximum amount of memory used by the backend process for temporary |
|
|
|
|
sorts. The <I>-S</I> value is measured in kilobytes, and the |
|
|
|
|
default is 512 (i.e. 512K).</P> |
|
|
|
|
<P>You can also use the <I>sort_mem</I> and <I>work_mem</I> options |
|
|
|
|
to increase the maximum amount of memory used by the backend processes |
|
|
|
|
for each temporary sort. The default is 1024 (i.e. 1MB).</P> |
|
|
|
|
|
|
|
|
|
<P>You can also use the <SMALL>CLUSTER</SMALL> command to group |
|
|
|
|
data in tables to match an index. See the <SMALL>CLUSTER</SMALL> |
|
|
|
|
@ -717,17 +719,18 @@ |
|
|
|
|
|
|
|
|
|
<P>If <I>postmaster</I> is running, start <I>psql</I> in one |
|
|
|
|
window, then find the <SMALL>PID</SMALL> of the <I>postgres</I> |
|
|
|
|
process used by <I>psql</I>. Use a debugger to attach to the |
|
|
|
|
<I>postgres</I> <SMALL>PID</SMALL>. You can set breakpoints in the |
|
|
|
|
debugger and issue queries from <I>psql</I>. If you are debugging |
|
|
|
|
<I>postgres</I> startup, you can set PGOPTIONS="-W n", then start |
|
|
|
|
<I>psql</I>. This will cause startup to delay for <I>n</I> seconds |
|
|
|
|
so you can attach to the process with the debugger, set any |
|
|
|
|
breakpoints, and continue through the startup sequence.</P> |
|
|
|
|
|
|
|
|
|
<P>The <I>postgres</I> program has <I>-s, -A</I>, and <I>-t</I> |
|
|
|
|
options that can be very useful for debugging and performance |
|
|
|
|
measurements.</P> |
|
|
|
|
process used by <I>psql</I> using <pre>SELECT pg_backend_pid()</pre>. |
|
|
|
|
Use a debugger to attach to the <I>postgres</I> <SMALL>PID</SMALL>. |
|
|
|
|
You can set breakpoints in the debugger and issue queries from |
|
|
|
|
<I>psql</I>. If you are debugging <I>postgres</I> startup, you can |
|
|
|
|
set PGOPTIONS="-W n", then start <I>psql</I>. This will cause startup |
|
|
|
|
to delay for <I>n</I> seconds so you can attach to the process with |
|
|
|
|
the debugger, set any breakpoints, and continue through the startup |
|
|
|
|
sequence.</P> |
|
|
|
|
|
|
|
|
|
<P>There are several <pre>log_*</pre> server configuration variables |
|
|
|
|
that enable printing of process statistics which can be very useful |
|
|
|
|
for debugging and performance measurements.</P> |
|
|
|
|
|
|
|
|
|
<P>You can also compile with profiling to see what functions are |
|
|
|
|
taking execution time. The backend profile files will be deposited |
|
|
|
|
@ -947,7 +950,8 @@ |
|
|
|
|
|
|
|
|
|
<H4><A name="4.8">4.8</A>) My queries are slow or don't make use of |
|
|
|
|
the indexes. Why?</H4> |
|
|
|
|
Indexes are not automatically used by every query. Indexes are only |
|
|
|
|
|
|
|
|
|
<P>Indexes are not automatically used by every query. Indexes are only |
|
|
|
|
used if the table is larger than a minimum size, and the query |
|
|
|
|
selects only a small percentage of the rows in the table. This is |
|
|
|
|
because the random disk access caused by an index scan can be |
|
|
|
|
@ -997,7 +1001,11 @@ |
|
|
|
|
<I>~*</I> do not utilise indexes. Instead, use functional |
|
|
|
|
indexes, which are described in section <a href="#4.12">4.12</a>.</LI> |
|
|
|
|
<LI>The default <I>C</I> locale must be used during |
|
|
|
|
<i>initdb</i>.</LI> |
|
|
|
|
<i>initdb</i> because it is not possible to know the next-greater |
|
|
|
|
character in a non-C locale. You can create a special |
|
|
|
|
<PRE>text_pattern_ops</PRE> index for such cases that work only |
|
|
|
|
for <PRE>LIKE</PRE> indexing. |
|
|
|
|
</LI> |
|
|
|
|
</UL> |
|
|
|
|
<P> |
|
|
|
|
|
|
|
|
|
@ -1169,8 +1177,8 @@ BYTEA bytea variable-length byte array (null-byte safe) |
|
|
|
|
value is made available via <I>$sth->{pg_oid_status}</I> after |
|
|
|
|
<I>$sth->execute()</I>. |
|
|
|
|
|
|
|
|
|
<H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and |
|
|
|
|
<I>nextval()</I> lead to a race condition with other users?</H4> |
|
|
|
|
<H4><A name="4.15.3">4.15.3</A>) Doesn't <I>currval()</I> |
|
|
|
|
lead to a race condition with other users?</H4> |
|
|
|
|
|
|
|
|
|
<P>No. <I>currval()</I> returns the current value assigned by your |
|
|
|
|
backend, not by all users.</P> |
|
|
|
|
|
Bruce Momjian
21 years ago