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@ -10,7 +10,7 @@ |
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alink="#0000ff"> |
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> |
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<P>Last updated: Thu Dec 5 00:47:26 EST 2002</P> |
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<P>Last updated: Fri Feb 14 09:03:00 EST 2003</P> |
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<P>Current maintainer: Bruce Momjian (<A href= |
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> |
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@ -18,10 +18,10 @@ |
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<P>The most recent version of this document can be viewed at <A |
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href= |
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"http://www.PostgreSQL.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P> |
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"http://www.ca.PostgreSQL.org/docs/faq-english.html">http://www.ca.PostgreSQL.org/docs/faq-english.html</A>.</P> |
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<P>Platform-specific questions are answered at <A href= |
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"http://www.PostgreSQL.org/users-lounge/docs/faq.html">http://www.PostgreSQL.org/users-lounge/docs/faq.html</A>.</P> |
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"http://www.ca.PostgreSQL.org/users-lounge/docs/faq.html">http://www.ca.PostgreSQL.org/users-lounge/docs/faq.html</A>.</P> |
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<HR> |
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<H2 align="center">General Questions</H2> |
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@ -314,11 +314,11 @@ |
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'#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P> |
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<P>A list of commercial support companies is available at <A href= |
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"http://www.PostgreSQL.org/users-lounge/commercial-support.html">http://www.PostgreSQL.org/users-lounge/commercial-support.html</A>.</P> |
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"http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html">http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html</A>.</P> |
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<H4><A name="1.7">1.7</A>) What is the latest release?</H4> |
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<P>The latest release of PostgreSQL is version 7.2.3.</P> |
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<P>The latest release of PostgreSQL is version 7.3.2.</P> |
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<P>We plan to have major releases every four months.</P> |
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@ -327,7 +327,7 @@ |
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<P>Several manuals, manual pages, and some small test examples are |
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included in the distribution. See the <I>/doc</I> directory. You |
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can also browse the manual online at <A href= |
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"http://www.PostgreSQL.org/users-lounge/docs/">http://www.PostgreSQL.org/users-lounge/docs/</A>.</P> |
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"http://www.ca.PostgreSQL.org/users-lounge/docs/">http://www.ca.PostgreSQL.org/users-lounge/docs/</A>.</P> |
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<P>There are two PostgreSQL books available online at <A href= |
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"http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A> |
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@ -536,8 +536,8 @@ |
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interface?</H4> |
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Yes, there are several graphical interfaces to PostgreSQL available. |
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These include PgAccess <a href="http://www.pgaccess.com"> |
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http://www.pgaccess.com</a>), PgAdmin II (<a |
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These include PgAccess <a href="http://www.pgaccess.org"> |
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http://www.pgaccess.org</a>), PgAdmin II (<a |
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href="http://www.pgadmin.org">http://www.pgadmin.org</a>, |
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Win32-only), RHDB Admin (<a |
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href="http://sources.redhat.com/rhdb/">http://sources.redhat.com/rhdb/ |
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@ -547,10 +547,6 @@ |
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http://phppgadmin.sourceforge.net/ </a>), a web-based interface to |
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PostgreSQL. |
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<P>We have a nice graphical user interface called PgAccess which can |
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also be used as a report generator. The Web page is |
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<A href="http://www.pgaccess.org/">http://www.pgaccess.org/</A>.</P> |
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<H4><A name="2.4">2.4</A>) What languages are able to communicate with |
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PostgreSQL?</H4> |
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@ -757,11 +753,6 @@ |
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the number of allowed backend processes is so your system won't run |
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out of resources.</P> |
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<P>In PostgreSQL versions prior to 6.5, the maximum number of |
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backends was 64, and changing it required a rebuild after altering |
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the MaxBackendId constant in |
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<I>include/storage/sinvaladt.h</I>.</P> |
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<H4><A name="3.9">3.9</A>) What is in the <I>pgsql_tmp</I> directory?</H4> |
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<P>This directory contains temporary files generated by the query |
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@ -947,6 +938,10 @@ |
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LIMIT 1; |
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</PRE> |
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<P>If you believe the optimizer is incorrect in choosing a |
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sequential scan, use <CODE>SET enable_seqscan TO 'off'</CODE> and |
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run tests to see if an index scan is indeed faster.</P> |
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<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or |
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<I>~</I>, indexes can only be used in certain circumstances:</P> |
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<UL> |
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@ -1039,10 +1034,10 @@ |
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<PRE> |
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Type Internal Name Notes |
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-------------------------------------------------- |
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"char" char 1 character |
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CHAR(n) bpchar blank padded to the specified fixed length |
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VARCHAR(n) varchar size specifies maximum length, no padding |
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CHAR(n) bpchar blank padded to the specified fixed length |
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TEXT text no specific upper limit on length |
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"char" char one character |
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BYTEA bytea variable-length byte array (null-byte safe) |
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</PRE> |
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@ -1056,11 +1051,13 @@ BYTEA bytea variable-length byte array (null-byte safe) |
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stored out-of-line by <SMALL>TOAST</SMALL>, so the space on disk |
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might also be less than expected.</P> |
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<P><SMALL>CHAR(n)</SMALL> is best when storing strings that are |
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usually the same length. <SMALL>VARCHAR(n)</SMALL> is best when |
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storing variable-length strings but it limits how long a string can |
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be. <SMALL>TEXT</SMALL> is for strings of unlimited length, maximum |
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1 gigabyte. <SMALL>BYTEA</SMALL> is for storing binary data, |
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<SMALL>VARCHAR(n)</SMALL> is best when storing variable-length |
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strings and it limits how long a string can be. <SMALL>TEXT</SMALL> |
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is for strings of unlimited length, with a maximum of one gigabyte. |
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<P><SMALL>CHAR(n)</SMALL> is for storing strings that are all the |
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same length. <SMALL>CHAR(n)</SMALL> pads with blanks to the specified |
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length, while <SMALL>VARCHAR(n)</SMALL> only stores the characters |
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supplied. <SMALL>BYTEA</SMALL> is for storing binary data, |
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particularly values that include <SMALL>NULL</SMALL> bytes. These |
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types have similar performance characteristics.</P> |
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@ -1286,7 +1283,7 @@ BYTEA bytea variable-length byte array (null-byte safe) |
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</PRE> |
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For this to be fast, <CODE>subcol</CODE> should be an indexed column. |
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We hope to fix this limitation in a future release. |
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This preformance problem will be fixed in 7.4. |
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<H4><A name="4.23">4.23</A>) How do I perform an outer join?</H4> |
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Bruce Momjian
24 years ago