Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Tue Feb 1 16:10:47 EST 2005
+ Last updated: Wed Feb 2 08:40:42 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
3.3) How do I tune the database engine for better performance?
3.4) What debugging features are available?
3.5) Why do I get "Sorry, too many clients" when trying to connect?
- 3.6) What is in the pgsql_tmp directory?
- 3.7) Why do I need to do a dump and restore to upgrade PostgreSQL
+ 3.6) Why do I need to do a dump and restore to upgrade PostgreSQL
releases?
- 3.8) What computer hardware should I use?
+ 3.7) What computer hardware should I use?
Operational Questions
processes it can start by changing the max_connections value in
postgresql.conf and restarting the postmaster.
- 3.6) What is in the pgsql_tmp directory?
-
- This directory contains 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 temporary files are created here to hold the extra data.
-
- The temporary files are usually deleted automatically, but might
- remain if a backend crashes during a sort. A stop and restart of the
- postmaster will remove files from those directories.
-
- 3.7) Why do I need to do a dump and restore to upgrade between major
+ 3.6) Why do I need to do a dump and restore to upgrade between major
PostgreSQL releases?
The PostgreSQL team makes only small changes between minor releases,
files. A dump outputs data in a generic format that can then be loaded
in using the new internal format.
- 3.8) What computer hardware should I use?
+ 3.7) What computer hardware should I use?
Because PC hardware is mostly compatible, people tend to believe that
all PC hardware is of equal quality. It is not. ECC RAM, SCSI, and
4.10) What is the difference between the various character types?
- Type Internal Name Notes
- VARCHAR(n) varchar size specifies maximum length, no padding
- CHAR(n) bpchar blank padded to the specified fixed length
- TEXT text no specific upper limit on length
- BYTEA bytea variable-length byte array (null-byte safe)
- "char" char one character
+ Type Internal Name Notes
+ VARCHAR(n) varchar size specifies maximum length, no padding
+ CHAR(n) bpchar blank padded to the specified fixed length
+ TEXT text no specific upper limit on length
+ BYTEA bytea variable-length byte array (null-byte safe)
+ "char" char one character
You will see the internal name when examining system catalogs and in
some error messages.
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Tue Feb 1 16:10:47 EST 2005</P>
+ <P>Last updated: Wed Feb 2 08:40:42 EST 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
<A href="#3.4">3.4</A>) What debugging features are available?<BR>
<A href="#3.5">3.5</A>) Why do I get <I>"Sorry, too many
clients"</I> when trying to connect?<BR>
- <A href="#3.6">3.6</A>) What is in the <I>pgsql_tmp</I>
- directory?<BR>
- <A href="#3.7">3.7</A>) Why do I need to do a dump and restore
+ <A href="#3.6">3.6</A>) Why do I need to do a dump and restore
to upgrade PostgreSQL releases?<BR>
- <A href="#3.8">3.8</A>) What computer hardware should I use?<BR>
+ <A href="#3.7">3.7</A>) What computer hardware should I use?<BR>
<H2 align="center">Operational Questions</H2>
<I>max_connections</I> value in <I>postgresql.conf</I> and
restarting the <I>postmaster</I>.</P>
- <H4><A name="3.6">3.6</A>) What is in the <I>pgsql_tmp</I> directory?</H4>
-
- <P>This directory contains temporary files generated by the query
- executor. For example, if a sort needs to be done to satisfy an
- <SMALL>ORDER BY</SMALL> and the sort requires more space than the
- backend's <I>-S</I> parameter allows, then temporary files are created
- here to hold the extra data.</P>
-
- <P>The temporary files are usually deleted automatically, but might
- remain if a backend crashes during a sort. A stop and restart of the
- <I>postmaster</I> will remove files from those directories.</P>
-
- <H4><A name="3.7">3.7</A>) Why do I need to do a dump and restore
+ <H4><A name="3.6">3.6</A>) Why do I need to do a dump and restore
to upgrade between major PostgreSQL releases?</H4>
<P>The PostgreSQL team makes only small changes between minor releases,
data in a generic format that can then be loaded in using the new internal
format.</P>
- <H4><A name="3.8">3.8</A>) What computer hardware should I use?</H4>
+ <H4><A name="3.7">3.7</A>) What computer hardware should I use?</H4>
<P>Because PC hardware is mostly compatible, people tend to believe that
all PC hardware is of equal quality. It is not. ECC RAM, SCSI, and
table, and a database?</H4>
<P>These are the limits:</P>
-<CENTER>
+<BLOCKQUOTE>
<TABLE BORDER=1>
<TR><TD>Maximum size for a database?</TD><TD>unlimited (32 TB databases
exist)</TD></TR>
<TR><TD>Maximum number of indexes on a
table?</TD><TD>unlimited</TD></TR>
</TABLE>
-</CENTER>
-<BR>
+</BLOCKQUOTE>
<P>Of course, these are not actually unlimited, but limited to
available disk space and memory/swap space. Performance may suffer
<H4><A name="4.10">4.10</A>) What is the difference between the
various character types?</H4>
-<CENTER>
+<BLOCKQUOTE>
<TABLE BORDER=1>
<TR><TH>Type</TH><TH>Internal Name</TH><TH>Notes</TH></TR>
<TR><TD>VARCHAR(n)</TD><TD>varchar</TD><TD>size specifies maximum
(null-byte safe)</TD></TR>
<TR><TD>"char"</TD><TD>char</TD><TD>one character</TD></TR>
</TABLE>
-</CENTER>
+</BLOCKQUOTE>
+
<P>You will see the internal name when examining system catalogs
and in some error messages.</P>
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