mirror of
https://git.postgresql.org/git/postgresql.git
synced 2025-03-07 19:47:50 +08:00
Brand 7.2.3.
This commit is contained in:
parent
9227bc5e5b
commit
4526d2183f
2
configure
vendored
2
configure
vendored
@ -615,7 +615,7 @@ ac_config_sub=$ac_aux_dir/config.sub
|
||||
ac_configure=$ac_aux_dir/configure # This should be Cygnus configure.
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VERSION='7.2.2'
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VERSION='7.2.3'
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cat >> confdefs.h <<EOF
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#define PG_VERSION "$VERSION"
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|
@ -28,7 +28,7 @@ AC_CONFIG_HEADER(src/include/pg_config.h)
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AC_PREREQ(2.13)
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AC_CONFIG_AUX_DIR(config)
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||||
|
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VERSION='7.2.2'
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||||
VERSION='7.2.3'
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||||
AC_SUBST(VERSION)
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AC_DEFINE_UNQUOTED(PG_VERSION, "$VERSION")
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||||
|
||||
|
142
doc/FAQ
142
doc/FAQ
@ -1,7 +1,7 @@
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||||
|
||||
Frequently Asked Questions (FAQ) for PostgreSQL
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||||
|
||||
Last updated: Mon Mar 18 14:34:57 EST 2002
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||||
Last updated: Mon Sep 30 23:28:35 EDT 2002
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||||
|
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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||||
|
||||
@ -53,6 +53,8 @@
|
||||
3.7) What debugging features are available?
|
||||
3.8) Why do I get "Sorry, too many clients" when trying to connect?
|
||||
3.9) What are the pg_sorttempNNN.NN files in my database directory?
|
||||
3.10) Why do I need to do a dump and restore to upgrade PostgreSQL
|
||||
releases?
|
||||
|
||||
Operational Questions
|
||||
|
||||
@ -63,8 +65,8 @@
|
||||
4.5) What is the maximum size for a row, a table, and a database?
|
||||
4.6) How much database disk space is required to store data from a
|
||||
typical text file?
|
||||
4.7) How do I find out what tables or indexes are defined in the
|
||||
database?
|
||||
4.7) How do I find out what tables, indexes, databases, and users are
|
||||
defined?
|
||||
4.8) My queries are slow or don't make use of the indexes. Why?
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||||
4.9) How do I see how the query optimizer is evaluating my query?
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||||
4.10) What is an R-tree index?
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||||
@ -91,6 +93,9 @@
|
||||
4.22) Why are my subqueries using IN so slow?
|
||||
4.23) How do I perform an outer join?
|
||||
4.24) How do I perform queries using multiple databases?
|
||||
4.25) How do I return multiple rows or columns from a function?
|
||||
4.26) Why can't I reliably create/drop temporary tables in PL/PgSQL
|
||||
functions?
|
||||
|
||||
Extending PostgreSQL
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||||
|
||||
@ -237,7 +242,7 @@
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||||
|
||||
1.7) What is the latest release?
|
||||
|
||||
The latest release of PostgreSQL is version 7.2.1.
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||||
The latest release of PostgreSQL is version 7.2.3.
|
||||
|
||||
We plan to have major releases every four months.
|
||||
|
||||
@ -320,29 +325,15 @@
|
||||
reduce lock contention.
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||||
|
||||
Performance
|
||||
PostgreSQL runs in two modes. Normal fsync mode flushes every
|
||||
completed transaction to disk, guaranteeing that if the OS
|
||||
crashes or loses power in the next few seconds, all your data
|
||||
is safely stored on disk. In this mode, we are slower than most
|
||||
commercial databases, partly because few of them do such
|
||||
conservative flushing to disk in their default modes. In
|
||||
no-fsync mode, we are usually faster than commercial databases,
|
||||
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.
|
||||
In comparison to MySQL or leaner database systems, we are
|
||||
slower on inserts/updates because we have transaction overhead.
|
||||
PostgreSQL has performance similar to other commercial and open
|
||||
source databases. it is faster for some things, slower for
|
||||
others. In comparison to MySQL or leaner database systems, we
|
||||
are slower on inserts/updates because of transaction overhead.
|
||||
Of course, MySQL does not have any of the features mentioned in
|
||||
the Features section above. We are built for flexibility and
|
||||
features, though we continue to improve performance through
|
||||
profiling and source code analysis. There is an interesting Web
|
||||
page comparing PostgreSQL to MySQL at
|
||||
http://openacs.org/why-not-mysql.html
|
||||
We handle each user connection by creating a Unix process.
|
||||
Backend processes share data buffers and locking information.
|
||||
With multiple CPUs, multiple backends can easily run on
|
||||
different CPUs.
|
||||
the Features section above. We are built for reliability and
|
||||
features, though we continue to improve performance in every
|
||||
release. There is an interesting Web page comparing PostgreSQL
|
||||
to MySQL at http://openacs.org/why-not-mysql.html
|
||||
|
||||
Reliability
|
||||
We realize that a DBMS must be reliable, or it is worthless. We
|
||||
@ -380,7 +371,8 @@
|
||||
Of course, this infrastructure is not cheap. There are a variety of
|
||||
monthly and one-time expenses that are required to keep it going. If
|
||||
you or your company has money it can donate to help fund this effort,
|
||||
please go to http://www.pgsql.com/pg_goodies and make a donation.
|
||||
please go to https://store.pgsql.com/shopping/index.php?id=1 and make
|
||||
a donation.
|
||||
|
||||
Although the web page mentions PostgreSQL, Inc, the "contributions"
|
||||
item is solely to support the PostgreSQL project and does not fund any
|
||||
@ -443,6 +435,9 @@
|
||||
* TCL (libpgtcl)
|
||||
* C Easy API (libpgeasy)
|
||||
* Embedded HTML (PHP from http://www.php.net)
|
||||
|
||||
Additional interfaces are available at
|
||||
http://www.postgresql.org/interfaces.html.
|
||||
_________________________________________________________________
|
||||
|
||||
Administrative Questions
|
||||
@ -570,7 +565,8 @@
|
||||
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.
|
||||
in the client's current directory. Linux requires a compile with
|
||||
-DLINUX_PROFILE for proper profiling.
|
||||
|
||||
3.8) Why do I get "Sorry, too many clients" when trying to connect?
|
||||
|
||||
@ -606,6 +602,21 @@
|
||||
The temporary 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.
|
||||
|
||||
3.10) 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,
|
||||
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
||||
However, major releases often change the internal format of system
|
||||
tables and data files. These changes are often complex, so we don't
|
||||
maintain backward compatability for data files. A dump outputs data in
|
||||
a generic format that can then be loaded in using the new internal
|
||||
format.
|
||||
|
||||
In releases where the on-disk format does not change, the pg_upgrade
|
||||
script can be used to upgrade without a dump/restore. The release
|
||||
notes mention whether pg_upgrade is available for the release.
|
||||
_________________________________________________________________
|
||||
|
||||
Operational Questions
|
||||
@ -635,19 +646,22 @@
|
||||
4.4) How do you remove a column from a table?
|
||||
|
||||
We do not support ALTER TABLE DROP COLUMN, but do this:
|
||||
BEGIN;
|
||||
LOCK TABLE old_table;
|
||||
SELECT ... -- select all columns but the one you want to remove
|
||||
INTO TABLE new_table
|
||||
FROM old_table;
|
||||
DROP TABLE old_table;
|
||||
ALTER TABLE new_table RENAME TO old_table;
|
||||
COMMIT;
|
||||
|
||||
4.5) What is the maximum size for a row, a table, and a database?
|
||||
|
||||
These are the limits:
|
||||
Maximum size for a database? unlimited (500 GB databases exist)
|
||||
Maximum size for a database? unlimited (1 TB databases exist)
|
||||
Maximum size for a table? 16 TB
|
||||
Maximum size for a row? unlimited in 7.1 and later
|
||||
Maximum size for a field? 1 GB in 7.1 and later
|
||||
Maximum size for a row? 1.6TB
|
||||
Maximum size for a field? 1 GB
|
||||
Maximum number of rows in a table? unlimited
|
||||
Maximum number of columns in a table? 250-1600 depending on column types
|
||||
Maximum number of indexes on a table? unlimited
|
||||
@ -695,10 +709,14 @@
|
||||
Indexes do not require as much overhead, but do contain the data that
|
||||
is being indexed, so they can be large also.
|
||||
|
||||
4.7) How do I find out what tables or indexes are defined in the database?
|
||||
NULLs are stored in bitmaps, so they use very little space.
|
||||
|
||||
4.7) How do I find out what tables, indexes, databases, and users are
|
||||
defined?
|
||||
|
||||
psql has a variety of backslash commands to show such information. Use
|
||||
\? to see them.
|
||||
\? to see them. There are also system tables beginning with pg_ that
|
||||
describe these too. Also, psql -l will list all databases.
|
||||
|
||||
Also try the file pgsql/src/tutorial/syscat.source. It illustrates
|
||||
many of the SELECTs needed to get information from the database system
|
||||
@ -709,7 +727,7 @@
|
||||
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 is sometimes slower than a
|
||||
random disk access caused by an index scan can be slower than a
|
||||
straight read through the table, or sequential scan.
|
||||
|
||||
To determine if an index should be used, PostgreSQL must have
|
||||
@ -724,12 +742,29 @@
|
||||
sequential scan followed by an explicit sort is usually faster than an
|
||||
index scan of a large table.
|
||||
However, LIMIT combined with ORDER BY often will use an index because
|
||||
only a small portion of the table is returned.
|
||||
only a small portion of the table is returned. In fact, though MAX()
|
||||
and MIN() don't use indexes, it is possible to retrieve such values
|
||||
using an index with ORDER BY and LIMIT:
|
||||
SELECT col
|
||||
FROM tab
|
||||
ORDER BY col [ DESC ]
|
||||
LIMIT 1
|
||||
|
||||
When using wild-card operators such as LIKE or ~, indexes can only be
|
||||
used if the beginning of the search is anchored to the start of the
|
||||
string. Therefore, to use indexes, LIKE patterns must not start with
|
||||
%, and ~(regular expression) patterns must start with ^.
|
||||
used in certain circumstances:
|
||||
* The beginning of the search string must be anchored to the start
|
||||
of the string, i.e.:
|
||||
|
||||
* LIKE patterns must not start with %.
|
||||
* ~ (regular expression) patterns must start with ^.
|
||||
|
||||
The search string can not start with a character class, e.g. [a-e].
|
||||
|
||||
Case-insensitive searches like ILIKE and ~* can not be used.
|
||||
Instead, use functional indexes, which are described later in this
|
||||
FAQ.
|
||||
|
||||
The default C local must be used during initdb.
|
||||
|
||||
4.9) How do I see how the query optimizer is evaluating my query?
|
||||
|
||||
@ -770,7 +805,7 @@
|
||||
|
||||
The ~ operator does regular expression matching, and ~* does
|
||||
case-insensitive regular expression matching. The case-insensitive
|
||||
variant of LIKE is called ILIKE in PostgreSQL 7.1 and later.
|
||||
variant of LIKE is called ILIKE.
|
||||
|
||||
Case-insensitive equality comparisons are normally expressed as:
|
||||
SELECT *
|
||||
@ -923,10 +958,9 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
|
||||
4.18) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()"?
|
||||
|
||||
If you are running a version older than 7.1, an upgrade may fix the
|
||||
problem. Also it is possible you have run out of virtual memory on
|
||||
your system, or your kernel has a low limit for certain resources. Try
|
||||
this before starting postmaster:
|
||||
You probably have run out of virtual memory on your system, or your
|
||||
kernel has a low limit for certain resources. Try this before starting
|
||||
postmaster:
|
||||
ulimit -d 262144
|
||||
limit datasize 256m
|
||||
|
||||
@ -979,8 +1013,8 @@ SELECT *
|
||||
|
||||
4.23) How do I perform an outer join?
|
||||
|
||||
PostgreSQL 7.1 and later supports outer joins using the SQL standard
|
||||
syntax. Here are two examples:
|
||||
PostgreSQL supports outer joins using the SQL standard syntax. Here
|
||||
are two examples:
|
||||
SELECT *
|
||||
FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
|
||||
|
||||
@ -1015,6 +1049,24 @@ SELECT *
|
||||
|
||||
Of course, a client can make simultaneous connections to different
|
||||
databases and merge the information that way.
|
||||
|
||||
4.25) How do I return multiple rows or columns from a function?
|
||||
|
||||
You can return result sets from PL/pgSQL functions using refcursors.
|
||||
See
|
||||
http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html,
|
||||
section 23.7.3.3.
|
||||
|
||||
4.26) Why can't I reliably create/drop temporary tables in PL/PgSQL
|
||||
functions?
|
||||
|
||||
PL/PgSQL caches function contents, and an unfortunate side effect is
|
||||
that if a PL/PgSQL function accesses a temporary table, and that table
|
||||
is later dropped and recreated, and the function called again, the
|
||||
function will fail because the cached function contents still point to
|
||||
the old temporary table. The solution is to use EXECUTE for temporary
|
||||
table access in PL/PgSQL. This will cause the query to be reparsed
|
||||
every time.
|
||||
_________________________________________________________________
|
||||
|
||||
Extending PostgreSQL
|
||||
|
@ -27,7 +27,7 @@ System Configuration
|
||||
|
||||
Operating System (example: Linux 2.0.26 ELF) :
|
||||
|
||||
PostgreSQL version (example: PostgreSQL-7.2.2): PostgreSQL-7.2.2
|
||||
PostgreSQL version (example: PostgreSQL-7.2.3): PostgreSQL-7.2.3
|
||||
|
||||
Compiler used (example: gcc 2.95.2) :
|
||||
|
||||
|
@ -14,7 +14,7 @@
|
||||
alink="#0000ff">
|
||||
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
|
||||
|
||||
<P>Last updated: Mon Mar 18 14:34:57 EST 2002</P>
|
||||
<P>Last updated: Mon Sep 30 23:28:35 EDT 2002</P>
|
||||
|
||||
<P>Current maintainer: Bruce Momjian (<A href=
|
||||
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
|
||||
@ -81,6 +81,8 @@
|
||||
clients"</I> when trying to connect?<BR>
|
||||
<A href="#3.9">3.9</A>) What are the <I>pg_sorttempNNN.NN</I>
|
||||
files in my database directory?<BR>
|
||||
<A href="#3.10">3.10</A>) Why do I need to do a dump and restore
|
||||
to upgrade PostgreSQL releases?<BR>
|
||||
|
||||
|
||||
<H2 align="center">Operational Questions</H2>
|
||||
@ -96,8 +98,8 @@
|
||||
table, and a database?<BR>
|
||||
<A href="#4.6">4.6</A>) How much database disk space is required
|
||||
to store data from a typical text file?<BR>
|
||||
<A href="#4.7">4.7</A>) How do I find out what tables or indexes
|
||||
are defined in the database?<BR>
|
||||
<A href="#4.7">4.7</A>) How do I find out what tables, indexes,
|
||||
databases, and users are defined?<BR>
|
||||
<A href="#4.8">4.8</A>) My queries are slow or don't make use of
|
||||
the indexes. Why?<BR>
|
||||
<A href="#4.9">4.9</A>) How do I see how the query optimizer is
|
||||
@ -137,6 +139,10 @@
|
||||
<A href="#4.23">4.23</A>) How do I perform an outer join?<BR>
|
||||
<A href="#4.24">4.24</A>) How do I perform queries using multiple
|
||||
databases?<BR>
|
||||
<A href="#4.25">4.25</A>) How do I return multiple rows or columns
|
||||
from a function?<BR>
|
||||
<A href="#4.26">4.26</A>) Why can't I reliably create/drop
|
||||
temporary tables in PL/PgSQL functions?<BR>
|
||||
|
||||
|
||||
<H2 align="center">Extending PostgreSQL</H2>
|
||||
@ -276,6 +282,7 @@
|
||||
subscribe
|
||||
end
|
||||
</PRE>
|
||||
|
||||
Digests are sent out to members of this list whenever the main list
|
||||
has received around 30k of messages.
|
||||
|
||||
@ -287,6 +294,7 @@
|
||||
subscribe
|
||||
end
|
||||
</PRE>
|
||||
|
||||
There is also a developers discussion mailing list available. To
|
||||
subscribe to this list, send email to <A href=
|
||||
"mailto:pgsql-hackers-request@PostgreSQL.org">pgsql-hackers-request@PostgreSQL.org</A>
|
||||
@ -312,7 +320,7 @@
|
||||
|
||||
<H4><A name="1.7">1.7</A>) What is the latest release?</H4>
|
||||
|
||||
<P>The latest release of PostgreSQL is version 7.2.1.</P>
|
||||
<P>The latest release of PostgreSQL is version 7.2.3.</P>
|
||||
|
||||
<P>We plan to have major releases every four months.</P>
|
||||
|
||||
@ -421,32 +429,18 @@
|
||||
|
||||
<DT><B>Performance</B></DT>
|
||||
|
||||
<DD>PostgreSQL runs in two modes. Normal <I>fsync</I> mode
|
||||
flushes every completed transaction to disk, guaranteeing that if
|
||||
the OS crashes or loses power in the next few seconds, all your
|
||||
data is safely stored on disk. In this mode, we are slower than
|
||||
most commercial databases, partly because few of them do such
|
||||
conservative flushing to disk in their default modes. In
|
||||
<I>no-fsync</I> mode, we are usually faster than commercial
|
||||
databases, 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.<BR>
|
||||
<BR>
|
||||
In comparison to MySQL or leaner database systems, we are slower
|
||||
on inserts/updates because we have transaction overhead. Of
|
||||
<DD>PostgreSQL has performance similar to other commercial and
|
||||
open source databases. it is faster for some things, slower for
|
||||
others. In comparison to MySQL or leaner database systems, we are
|
||||
slower on inserts/updates because of transaction overhead. Of
|
||||
course, MySQL does not have any of the features mentioned in the
|
||||
<I>Features</I> section above. We are built for flexibility and
|
||||
features, though we continue to improve performance through
|
||||
profiling and source code analysis. There is an interesting Web
|
||||
page comparing PostgreSQL to MySQL at <A href=
|
||||
"http://openacs.org/why-not-mysql.html">http://openacs.org/why-not-mysql.html</A><BR>
|
||||
<I>Features</I> section above. We are built for reliability and
|
||||
features, though we continue to improve performance in every
|
||||
release. There is an interesting Web page comparing PostgreSQL to
|
||||
MySQL at <A href= "http://openacs.org/why-not-mysql.html">
|
||||
|
||||
http://openacs.org/why-not-mysql.html</A><BR>
|
||||
|
||||
<BR>
|
||||
We handle each user connection by creating a Unix process.
|
||||
Backend processes share data buffers and locking information.
|
||||
With multiple CPUs, multiple backends can easily run on different
|
||||
CPUs.<BR>
|
||||
<BR>
|
||||
</DD>
|
||||
|
||||
@ -499,7 +493,8 @@
|
||||
of monthly and one-time expenses that are required to keep it
|
||||
going. If you or your company has money it can donate to help fund
|
||||
this effort, please go to <A href=
|
||||
"http://www.pgsql.com/pg_goodies">http://www.pgsql.com/pg_goodies</A>
|
||||
"https://store.pgsql.com/shopping/index.php?id=1">
|
||||
https://store.pgsql.com/shopping/index.php?id=1</A>
|
||||
and make a donation.</P>
|
||||
|
||||
<P>Although the web page mentions PostgreSQL, Inc, the
|
||||
@ -588,6 +583,10 @@
|
||||
<LI>Embedded <SMALL>HTML</SMALL> (<A href=
|
||||
"http://www.php.net">PHP from http://www.php.net</A>)</LI>
|
||||
</UL>
|
||||
<P>Additional interfaces are available at <a
|
||||
href="http://www.postgresql.org/interfaces.html">
|
||||
http://www.postgresql.org/interfaces.html.</A>
|
||||
</P>
|
||||
<HR>
|
||||
|
||||
<H2 align="center">Administrative Questions</H2>
|
||||
@ -740,7 +739,8 @@
|
||||
<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.</P>
|
||||
file will be put in the client's current directory. Linux requires
|
||||
a compile with <I>-DLINUX_PROFILE</I> for proper profiling.</P>
|
||||
|
||||
<H4><A name="3.8">3.8</A>) Why do I get <I>"Sorry, too many
|
||||
clients"</I> when trying to connect?</H4>
|
||||
@ -785,6 +785,23 @@
|
||||
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.</P>
|
||||
|
||||
<H4><A name="3.10">3.10</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,
|
||||
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
|
||||
However, major releases often change the internal format of system
|
||||
tables and data files. These changes are often complex, so we don't
|
||||
maintain backward compatability for data files. A dump outputs data
|
||||
in a generic format that can then be loaded in using the new internal
|
||||
format.
|
||||
|
||||
<P>In releases where the on-disk format does not change, the
|
||||
<i>pg_upgrade</i> script can be used to upgrade without a dump/restore.
|
||||
The release notes mention whether <i>pg_upgrade</i> is available for the
|
||||
release.
|
||||
|
||||
<HR>
|
||||
|
||||
<H2 align="center">Operational Questions</H2>
|
||||
@ -824,11 +841,14 @@
|
||||
<P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
|
||||
this:</P>
|
||||
<PRE>
|
||||
BEGIN;
|
||||
LOCK TABLE old_table;
|
||||
SELECT ... -- select all columns but the one you want to remove
|
||||
INTO TABLE new_table
|
||||
FROM old_table;
|
||||
DROP TABLE old_table;
|
||||
ALTER TABLE new_table RENAME TO old_table;
|
||||
COMMIT;
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.5">4.5</A>) What is the maximum size for a row, a
|
||||
@ -836,14 +856,15 @@
|
||||
|
||||
<P>These are the limits:</P>
|
||||
<PRE>
|
||||
Maximum size for a database? unlimited (500 GB databases exist)
|
||||
Maximum size for a database? unlimited (1 TB databases exist)
|
||||
Maximum size for a table? 16 TB
|
||||
Maximum size for a row? unlimited in 7.1 and later
|
||||
Maximum size for a field? 1 GB in 7.1 and later
|
||||
Maximum size for a row? 1.6TB
|
||||
Maximum size for a field? 1 GB
|
||||
Maximum number of rows in a table? unlimited
|
||||
Maximum number of columns in a table? 250-1600 depending on column types
|
||||
Maximum number of indexes on a table? unlimited
|
||||
</PRE>
|
||||
|
||||
Of course, these are not actually unlimited, but limited to
|
||||
available disk space and memory/swap space. Performance may suffer
|
||||
when these values get unusually large.
|
||||
@ -890,11 +911,16 @@
|
||||
<P>Indexes do not require as much overhead, but do contain the data
|
||||
that is being indexed, so they can be large also.</P>
|
||||
|
||||
<H4><A name="4.7">4.7</A>) How do I find out what tables or indexes
|
||||
are defined in the database?</H4>
|
||||
<P><SMALL>NULL</SMALL>s are stored in bitmaps, so they
|
||||
use very little space.</P>
|
||||
|
||||
<H4><A name="4.7">4.7</A>) How do I find out what tables, indexes,
|
||||
databases, and users are defined?</H4>
|
||||
|
||||
<P><I>psql</I> has a variety of backslash commands to show such
|
||||
information. Use \? to see them.</P>
|
||||
information. Use \? to see them. There are also system tables
|
||||
beginning with <I>pg_</I> that describe these too. Also, <I>psql
|
||||
-l</I> will list all databases.</P>
|
||||
|
||||
<P>Also try the file <I>pgsql/src/tutorial/syscat.source</I>. It
|
||||
illustrates many of the <SMALL>SELECT</SMALL>s needed to get
|
||||
@ -905,7 +931,7 @@
|
||||
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 is sometimes
|
||||
because the random disk access caused by an index scan can be
|
||||
slower than a straight read through the table, or sequential scan.
|
||||
|
||||
<P>To determine if an index should be used, PostgreSQL must have
|
||||
@ -922,13 +948,35 @@
|
||||
usually faster than an index scan of a large table.</P>
|
||||
However, <SMALL>LIMIT</SMALL> combined with <SMALL>ORDER BY</SMALL>
|
||||
often will use an index because only a small portion of the table
|
||||
is returned.
|
||||
is returned. In fact, though MAX() and MIN() don't use indexes,
|
||||
it is possible to retrieve such values using an index with ORDER BY
|
||||
and LIMIT:
|
||||
<PRE>
|
||||
SELECT col
|
||||
FROM tab
|
||||
ORDER BY col [ DESC ]
|
||||
LIMIT 1
|
||||
</PRE>
|
||||
|
||||
<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or
|
||||
<I>~</I>, indexes can only be used if the beginning of the search
|
||||
is anchored to the start of the string. Therefore, to use indexes,
|
||||
<SMALL>LIKE</SMALL> patterns must not start with <I>%</I>, and
|
||||
<I>~</I>(regular expression) patterns must start with <I>^</I>.</P>
|
||||
<I>~</I>, indexes can only be used in certain circumstances:
|
||||
<UL>
|
||||
<LI>The beginning of the search string must be anchored to the start
|
||||
of the string, i.e.:</LI>
|
||||
<UL>
|
||||
<LI><SMALL>LIKE</SMALL> patterns must not start with <I>%.</I></LI>
|
||||
<LI><I>~</I> (regular expression) patterns must start with
|
||||
<I>^.</I></LI>
|
||||
</UL>
|
||||
<LI>The search string can not start with a character class,
|
||||
e.g. [a-e].</LI>
|
||||
<LI>Case-insensitive searches like <SMALL>ILIKE</SMALL> and
|
||||
<I>~*</I> can not be used. Instead, use functional
|
||||
indexes, which are described later in this FAQ.</LI>
|
||||
<LI>The default <I>C</I> local must be used during
|
||||
<i>initdb.</i></LI>
|
||||
</UL>
|
||||
<P>
|
||||
|
||||
<H4><A name="4.9">4.9</A>) How do I see how the query optimizer is
|
||||
evaluating my query?</H4>
|
||||
@ -975,7 +1023,7 @@
|
||||
<P>The <I>~</I> operator does regular expression matching, and
|
||||
<I>~*</I> does case-insensitive regular expression matching. The
|
||||
case-insensitive variant of <SMALL>LIKE</SMALL> is called
|
||||
<SMALL>ILIKE</SMALL> in PostgreSQL 7.1 and later.</P>
|
||||
<SMALL>ILIKE</SMALL>.</P>
|
||||
|
||||
<P>Case-insensitive equality comparisons are normally expressed
|
||||
as:</P>
|
||||
@ -983,13 +1031,12 @@
|
||||
SELECT *
|
||||
FROM tab
|
||||
WHERE lower(col) = 'abc'
|
||||
|
||||
</PRE>
|
||||
|
||||
This will not use an standard index. However, if you create a
|
||||
functional index, it will be used:
|
||||
<PRE>
|
||||
CREATE INDEX tabindex on tab (lower(col));
|
||||
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.13">4.13</A>) In a query, how do I detect if a field
|
||||
@ -1039,6 +1086,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
name TEXT
|
||||
);
|
||||
</PRE>
|
||||
|
||||
is automatically translated into this:
|
||||
<PRE>
|
||||
CREATE SEQUENCE person_id_seq;
|
||||
@ -1048,6 +1096,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
);
|
||||
CREATE UNIQUE INDEX person_id_key ON person ( id );
|
||||
</PRE>
|
||||
|
||||
See the <I>create_sequence</I> manual page for more information
|
||||
about sequences. You can also use each row's <I>OID</I> field as a
|
||||
unique value. However, if you need to dump and reload the database,
|
||||
@ -1066,6 +1115,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
new_id = output of "SELECT nextval('person_id_seq')"
|
||||
INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal');
|
||||
</PRE>
|
||||
|
||||
You would then also have the new value stored in
|
||||
<CODE>new_id</CODE> for use in other queries (e.g., as a foreign
|
||||
key to the <CODE>person</CODE> table). Note that the name of the
|
||||
@ -1081,6 +1131,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
INSERT INTO person (name) VALUES ('Blaise Pascal');
|
||||
new_id = output of "SELECT currval('person_id_seq')";
|
||||
</PRE>
|
||||
|
||||
Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A>
|
||||
returned from the <SMALL>INSERT</SMALL> statement to look up the
|
||||
default value, though this is probably the least portable approach.
|
||||
@ -1180,14 +1231,14 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
<H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR:
|
||||
Memory exhausted in AllocSetAlloc()"</I>?</H4>
|
||||
|
||||
<P>If you are running a version older than 7.1, an upgrade may fix
|
||||
the problem. Also it is possible you have run out of virtual memory
|
||||
on your system, or your kernel has a low limit for certain
|
||||
resources. Try this before starting <I>postmaster</I>:</P>
|
||||
<P>You probably have run out of virtual memory on your system,
|
||||
or your kernel has a low limit for certain resources. Try this
|
||||
before starting <I>postmaster</I>:</P>
|
||||
<PRE>
|
||||
ulimit -d 262144
|
||||
limit datasize 256m
|
||||
</PRE>
|
||||
|
||||
Depending on your shell, only one of these may succeed, but it will
|
||||
set your process data segment limit much higher and perhaps allow
|
||||
the query to complete. This command applies to the current process,
|
||||
@ -1246,12 +1297,13 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
|
||||
</CODE>
|
||||
</PRE>
|
||||
|
||||
We hope to fix this limitation in a future release.
|
||||
|
||||
<H4><A name="4.23">4.23</A>) How do I perform an outer join?</H4>
|
||||
|
||||
<P>PostgreSQL 7.1 and later supports outer joins using the SQL
|
||||
standard syntax. Here are two examples:</P>
|
||||
<P>PostgreSQL supports outer joins using the SQL standard syntax.
|
||||
Here are two examples:</P>
|
||||
<PRE>
|
||||
SELECT *
|
||||
FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
|
||||
@ -1297,6 +1349,26 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
|
||||
<P>Of course, a client can make simultaneous connections to
|
||||
different databases and merge the information that way.</P>
|
||||
|
||||
<H4><A name="4.25">4.25</A>) How do I return multiple rows or
|
||||
columns from a function?</H4>
|
||||
|
||||
<P>You can return result sets from PL/pgSQL functions using
|
||||
<I>refcursors</I>. See <A href=
|
||||
"http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html">
|
||||
http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html,</A>
|
||||
section 23.7.3.3.</P>
|
||||
|
||||
<H4><A name="4.26">4.26</A>) Why can't I reliably create/drop
|
||||
temporary tables in PL/PgSQL functions?</H4>
|
||||
PL/PgSQL caches function contents, and an unfortunate side effect
|
||||
is that if a PL/PgSQL function accesses a temporary table, and that
|
||||
table is later dropped and recreated, and the function called
|
||||
again, the function will fail because the cached function contents
|
||||
still point to the old temporary table. The solution is to use
|
||||
<SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This
|
||||
will cause the query to be reparsed every time.
|
||||
|
||||
<HR>
|
||||
|
||||
<H2 align="center">Extending PostgreSQL</H2>
|
||||
|
@ -3,5 +3,5 @@ Update this file to propagate correct current version numbers to the
|
||||
documentation. In text, use for example &version; to refer to them.
|
||||
-->
|
||||
|
||||
<!entity version "7.2.2">
|
||||
<!entity version "7.2.3">
|
||||
<!entity majorversion "7.2">
|
||||
|
@ -3,8 +3,8 @@
|
||||
/*
|
||||
* Parts of pg_config.h that you get with autoconf on other systems
|
||||
*/
|
||||
#define PG_VERSION "7.2.2"
|
||||
#define PG_VERSION_STR "7.2.2 (win32)"
|
||||
#define PG_VERSION "7.2.3"
|
||||
#define PG_VERSION_STR "7.2.3 (win32)"
|
||||
|
||||
#define SYSCONFDIR ""
|
||||
|
||||
|
@ -1,8 +1,8 @@
|
||||
#include <winver.h>
|
||||
|
||||
VS_VERSION_INFO VERSIONINFO
|
||||
FILEVERSION 7,2,2,0
|
||||
PRODUCTVERSION 7,2,2,0
|
||||
FILEVERSION 7,2,3,0
|
||||
PRODUCTVERSION 7,2,3,0
|
||||
FILEFLAGSMASK 0x3fL
|
||||
FILEFLAGS 0x0L
|
||||
FILEOS 0x40004L
|
||||
@ -16,14 +16,14 @@ BEGIN
|
||||
VALUE "Comments", "\0"
|
||||
VALUE "CompanyName", " \0"
|
||||
VALUE "FileDescription", "PostgreSQL C++ Access Library\0"
|
||||
VALUE "FileVersion", "7, 2, 2, 0\0"
|
||||
VALUE "FileVersion", "7, 2, 3, 0\0"
|
||||
VALUE "InternalName", "libpq++\0"
|
||||
VALUE "LegalCopyright", "Copyright © 2000\0"
|
||||
VALUE "LegalTrademarks", "\0"
|
||||
VALUE "OriginalFilename", "libpq++.dll\0"
|
||||
VALUE "PrivateBuild", "\0"
|
||||
VALUE "ProductName", "PostgreSQL\0"
|
||||
VALUE "ProductVersion", "7, 2, 2, 0\0"
|
||||
VALUE "ProductVersion", "7, 2, 3, 0\0"
|
||||
VALUE "SpecialBuild", "\0"
|
||||
END
|
||||
END
|
||||
|
@ -1,8 +1,8 @@
|
||||
#include <winver.h>
|
||||
|
||||
VS_VERSION_INFO VERSIONINFO
|
||||
FILEVERSION 7,2,2,0
|
||||
PRODUCTVERSION 7,2,2,0
|
||||
FILEVERSION 7,2,3,0
|
||||
PRODUCTVERSION 7,2,3,0
|
||||
FILEFLAGSMASK 0x3fL
|
||||
FILEFLAGS 0
|
||||
FILEOS VOS__WINDOWS32
|
||||
@ -15,13 +15,13 @@ BEGIN
|
||||
BEGIN
|
||||
VALUE "CompanyName", "\0"
|
||||
VALUE "FileDescription", "PostgreSQL Access Library\0"
|
||||
VALUE "FileVersion", "7, 2, 2, 0\0"
|
||||
VALUE "FileVersion", "7, 2, 3, 0\0"
|
||||
VALUE "InternalName", "libpq\0"
|
||||
VALUE "LegalCopyright", "Copyright (C) 2000\0"
|
||||
VALUE "LegalTrademarks", "\0"
|
||||
VALUE "OriginalFilename", "libpq.dll\0"
|
||||
VALUE "ProductName", "PostgreSQL\0"
|
||||
VALUE "ProductVersion", "7, 2, 2, 0\0"
|
||||
VALUE "ProductVersion", "7, 2, 3, 0\0"
|
||||
END
|
||||
END
|
||||
BLOCK "VarFileInfo"
|
||||
|
Loading…
Reference in New Issue
Block a user