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Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Mon May 30 09:11:03 EDT 2005
Last updated: Fri Sep 16 14:07:22 EDT 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@ -79,13 +79,16 @@
4.19) Why do I get "relation with OID ##### does not exist" errors
when accessing temporary tables in PL/PgSQL functions?
4.20) What replication solutions are available?
4.21) Why are my table and column names not recognized in my query?
_________________________________________________________________
General Questions
1.1) What is PostgreSQL? How is it pronounced?
PostgreSQL is pronounced Post-Gres-Q-L, also called just Postgres.
PostgreSQL is pronounced Post-Gres-Q-L, and is also sometimes referred
to as just Postgres. An audio file is available in MP3 format for
those would like to hear the pronunciation.
PostgreSQL is an object-relational database system that has the
features of traditional commercial database systems with enhancements
@ -179,7 +182,7 @@
1.7) What is the latest release?
The latest release of PostgreSQL is version 8.0.2.
The latest release of PostgreSQL is version 8.0.3.
We plan to have a major release every year, with minor releases every
few months.
@ -469,6 +472,12 @@
The maximum table size and maximum number of columns can be quadrupled
by increasing the default block size to 32k.
One limitation is that indexes can not be created on columns longer
than about 2,000 characters. Fortunately, such indexes are rarely
needed. Uniqueness is best guaranteed by a funtion index of an MD5
hash of the long column, and full text indexing allows for searching
of words within the column.
4.5) How much database disk space is required to store data from a typical
text file?
@ -480,23 +489,23 @@
twenty bytes in length. The flat file would be 2.8 MB. The size of the
PostgreSQL database file containing this data can be estimated as 6.4
MB:
32 bytes: each row header (approximate)
28 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
60 bytes per row
56 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 136 rows per database page (rounded down)
60 bytes per row
------------------- = 146 rows per database page (rounded down)
56 bytes per row
100000 data rows
-------------------- = 735 database pages (rounded up)
128 rows per page
-------------------- = 685 database pages (rounded up)
146 rows per page
735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
685 database pages * 8192 bytes per page = 5,611,520 bytes (5.6 MB)
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
@ -576,6 +585,11 @@
expresssion index, it will be used:
CREATE INDEX tabindex ON tab (lower(col));
If the above index is created as UNIQUE, though the column can store
upper and lowercase characters, it can not have identical values that
differ only in case. To force a particular case to be stored in the
column, use a CHECK constraint or a trigger.
4.9) In a query, how do I detect if a field is NULL? How can I sort on
whether a field is NULL or not?
@ -774,3 +788,16 @@
There are also commercial and hardware-based replication solutions
available supporting a variety of replication models.
4.21) Why are my table and column names not recognized in my query?
The most common cause is the use of double-quotes around table or
column names during table creation. When double-quotes are used, table
and column names (called identifiers) are stored case-sensitive,
meaning you must use double-quotes when referencing the names in a
query. Some interfaces, like pgAdmin, automatically double-quote
identifiers during table creation. So, for identifiers to be
recognized, you must either:
* Avoid double-quoting identifiers when creating tables
* Use only lowercase characters in identifiers
* Double-quote identifiers when referencing them in queries

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@ -1,5 +1,5 @@
From: Zeugswetter Andreas <ZeugswetterA@spardat.at>
$Date: 2005/07/30 03:39:40 $
$Date: 2005/09/22 22:14:10 $
On AIX 4.3.2 PostgreSQL compiled with the native IBM compiler xlc
(vac.C 5.0.1) passes all regression tests. Other versions of OS and

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@ -1,7 +1,7 @@
Developer's Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Sat May 14 12:26:01 EDT 2005
Last updated: Mon Sep 19 21:28:08 EDT 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@ -101,7 +101,7 @@ General Questions
important to get community feeback on your proposal before starting
work. Failure to do so might mean your patch is rejected.
A web site is maintained for patches that are ready to be applied,
A web site is maintained for patches awaiting review,
http://momjian.postgresql.org/cgi-bin/pgpatches, and those that are
being kept for the next release,
http://momjian.postgresql.org/cgi-bin/pgpatches2.
@ -806,6 +806,6 @@ typedef struct nameData
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 client's current directory. Linux requires a compile with
pgsql/data directory. The client profile file will be put in the
client's current directory. Linux requires a compile with
-DLINUX_PROFILE for proper profiling.

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@ -6,7 +6,7 @@
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
The most recent version of this document can be viewed at
http://momjian.postgresql.org/main/writings/pgsql/project/win32.html.
http://www.postgresql.org/docs/faqs.FAQ_MINGW.html.
The FAQ for running PostgreSQL on native Win32 is at
http://pginstaller.projects.postgresql.org/FAQ_windows.html.

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@ -10,7 +10,7 @@
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Mon May 30 09:11:03 EDT 2005</P>
<P>Last updated: Fri Sep 16 14:07:22 EDT 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
@ -26,7 +26,7 @@
<HR>
<H2 align="center">General Questions</H2>
<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR>
<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR>
<A href="#1.2">1.2</A>) What is the copyright of PostgreSQL?<BR>
<A href="#1.3">1.3</A>) What platforms does PostgreSQL support?<BR>
<A href="#1.4">1.4</A>) Where can I get PostgreSQL?<BR>
@ -116,7 +116,9 @@
does not exist" errors when accessing temporary tables in PL/PgSQL
functions?<BR>
<A href="#4.20">4.20</A>) What replication solutions are available?<BR>
<A href="#4.21">4.21</A>) Why are my table and column names not
recognized in my query?<BR>
<HR>
@ -124,8 +126,10 @@
<H3><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H3>
<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, also called just
<I>Postgres</I>.</P>
<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, and is also sometimes
referred to as just <I>Postgres</I>. An audio file is available in
<a href="http://www.postgresql.org/files/postgresql.mp3">MP3 format</a> for
those would like to hear the pronunciation.</P>
<P>PostgreSQL is an object-relational database system that has the
features of traditional commercial database systems with
@ -231,7 +235,7 @@
<H3><A name="1.7">1.7</A>) What is the latest release?</H3>
<P>The latest release of PostgreSQL is version 8.0.2.</P>
<P>The latest release of PostgreSQL is version 8.0.3.</P>
<P>We plan to have a major release every year, with minor releases
every few months.</P>
@ -613,6 +617,12 @@ table?</TD><TD>unlimited</TD></TR>
<P>The maximum table size and maximum number of columns can be
quadrupled by increasing the default block size to 32k.</P>
<P>One limitation is that indexes can not be created on columns
longer than about 2,000 characters. Fortunately, such indexes are
rarely needed. Uniqueness is best guaranteed by a funtion index
of an MD5 hash of the long column, and full text indexing
allows for searching of words within the column.</P>
<H3><A name="4.5">4.5</A>) How much database disk space is required
to store data from a typical text file?</H3>
@ -625,23 +635,23 @@ table?</TD><TD>unlimited</TD></TR>
The size of the PostgreSQL database file containing this data can
be estimated as 6.4 MB:</P>
<PRE>
32 bytes: each row header (approximate)
28 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
60 bytes per row
56 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 136 rows per database page (rounded down)
60 bytes per row
------------------- = 146 rows per database page (rounded down)
56 bytes per row
100000 data rows
-------------------- = 735 database pages (rounded up)
128 rows per page
-------------------- = 685 database pages (rounded up)
146 rows per page
735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
685 database pages * 8192 bytes per page = 5,611,520 bytes (5.6 MB)
</PRE>
<P>Indexes do not require as much overhead, but do contain the data
@ -740,7 +750,12 @@ table?</TD><TD>unlimited</TD></TR>
<PRE>
CREATE INDEX tabindex ON tab (lower(col));
</PRE>
<P>If the above index is created as <SMALL>UNIQUE</SMALL>, though
the column can store upper and lowercase characters, it can not have
identical values that differ only in case. To force a particular
case to be stored in the column, use a <SMALL>CHECK</SMALL>
constraint or a trigger.</P>
<H3><A name="4.9">4.9</A>) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL>
NULL</SMALL> or not?</H3>
@ -1000,5 +1015,22 @@ length</TD></TR>
<P>There are also commercial and hardware-based replication solutions
available supporting a variety of replication models.</P>
<H3><A name="4.21">4.21</A>) Why are my table and column names not
recognized in my query?</H3>
<P>The most common cause is the use of double-quotes around table or
column names during table creation. When double-quotes are used,
table and column names (called identifiers) are stored <a
href="http://www.postgresql.org/docs/8.0/static/sql-syntax.html#SQL-
SYNTAX-IDENTIFIERS">case-sensitive</a>, meaning you must use
double-quotes when referencing the names in a query. Some interfaces,
like pgAdmin, automatically double-quote identifiers during table
creation. So, for identifiers to be recognized, you must either:
<UL>
<LI>Avoid double-quoting identifiers when creating tables</LI>
<LI>Use only lowercase characters in identifiers</LI>
<LI>Double-quote identifiers when referencing them in queries</LI>
</UL>
</BODY>
</HTML>

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@ -13,7 +13,7 @@
<H1>Developer's Frequently Asked Questions (FAQ) for
PostgreSQL</H1>
<P>Last updated: Sat May 14 12:26:01 EDT 2005</P>
<P>Last updated: Mon Sep 19 21:28:08 EDT 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@ -147,11 +147,11 @@
before starting work. Failure to do so might mean your patch is
rejected.</P>
<P>A web site is maintained for patches that are ready to be applied,
<P>A web site is maintained for patches awaiting review,
<a href="http://momjian.postgresql.org/cgi-bin/pgpatches">
http://momjian.postgresql.org/cgi-bin/pgpatches</a>, and
those that are being kept for the next release,
<a href="http://momjian.postgresql.org/cgi-bin/pgpatches2">
<a href="http://momjian.postgresql.org/cgi-bin/pgpatches_hold">
http://momjian.postgresql.org/cgi-bin/pgpatches2</a>.</P>
<H3><A name="1.5">1.5</A>) I've developed a patch, what next?</H3>
@ -992,9 +992,9 @@
<P>You can also compile with profiling to see what functions are
taking execution time. The backend profile files will be deposited
in the <I>pgsql/data/base/dbname</I> directory. The client profile
file will be put in the client's current directory. Linux requires
a compile with <I>-DLINUX_PROFILE</I> for proper profiling.</P>
in the <I>pgsql/data</I> directory. The client profile file will be
put in the client's current directory. Linux requires a compile with
<I>-DLINUX_PROFILE</I> for proper profiling.</P>
</BODY>
</HTML>

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@ -14,8 +14,8 @@
</P>
<P>The most recent version of this document can be viewed at <A href=
"http://momjian.postgresql.org/main/writings/pgsql/project/win32.html">
http://momjian.postgresql.org/main/writings/pgsql/project/win32.html</A>.</P>
"http://www.postgresql.org/docs/faqs.FAQ_MINGW.html">
http://www.postgresql.org/docs/faqs.FAQ_MINGW.html</A>.</P>
<P>The FAQ for running PostgreSQL on native Win32 is at <A href=
"http://pginstaller.projects.postgresql.org/FAQ_windows.html">