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Hot Standby documentation updates

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Greg Smith
This commit is contained in:
Bruce Momjian 2010-02-19 00:15:25 +00:00
parent a232f30f05
commit a70d039104
6 changed files with 75 additions and 62 deletions
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4
doc/src/sgml/backup.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.141 2010/02/09 16:50:25 heikki Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.142 2010/02/19 00:15:25 momjian Exp $ -->
<chapter id="backup">
<title>Backup and Restore</title>
@ -126,7 +126,7 @@ psql <replaceable class="parameter">dbname</replaceable> &lt; <replaceable class
execute after an SQL error is encountered. You might wish to run
<application>psql</application> with
the <literal>ON_ERROR_STOP</> variable set to alter that
behaviour and have <application>psql</application> exit with an
behavior and have <application>psql</application> exit with an
exit status of 3 if an SQL error occurs:
<programlisting>
psql --set ON_ERROR_STOP=on dbname &lt; infile

4
doc/src/sgml/ecpg.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/ecpg.sgml,v 1.96 2010/02/17 04:19:37 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/ecpg.sgml,v 1.97 2010/02/19 00:15:25 momjian Exp $ -->
<chapter id="ecpg">
<title><application>ECPG</application> - Embedded <acronym>SQL</acronym> in C</title>
@ -2882,7 +2882,7 @@ struct sqlname
program and most of the additional functions of the <productname>Informix</productname> compatibility
mode allow you to operate on those C host program types. Note however that
the extent of the compatibility is limited. It does not try to copy <productname>Informix</productname>
behaviour; it allows you to do more or less the same operations and gives
behavior; it allows you to do more or less the same operations and gives
you functions that have the same name and the same basic behavior but it is
no drop-in replacement if you are using <productname>Informix</productname> at the moment. Moreover,
some of the data types are different. For example,

6
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.504 2010/02/16 22:34:42 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.505 2010/02/19 00:15:25 momjian Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -13801,8 +13801,8 @@ SELECT (pg_stat_file('filename')).modification;
function, <function>suppress_redundant_updates_trigger</>,
which will prevent any update
that does not actually change the data in the row from taking place, in
contrast to the normal behaviour which always performs the update
regardless of whether or not the data has changed. (This normal behaviour
contrast to the normal behavior which always performs the update
regardless of whether or not the data has changed. (This normal behavior
makes updates run faster, since no checking is required, and is also
useful in certain cases.)
</para>

117
doc/src/sgml/high-availability.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.46 2010/02/18 04:14:38 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.47 2010/02/19 00:15:25 momjian Exp $ -->
<chapter id="high-availability">
<title>High Availability, Load Balancing, and Replication</title>
@ -1056,8 +1056,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
is useful for both log shipping replication and for restoring a backup
to an exact state with great precision.
The term Hot Standby also refers to the ability of the server to move
from recovery through to normal running while users continue running
queries and/or continue their connections.
from recovery through to normal operation while users continue running
queries and/or keep their connections open.
</para>
<para>
@ -1082,7 +1082,7 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
return differing results. Eventually, the standby will be
consistent with the primary.
Queries executed on the standby will be correct with regard to the transactions
that had been recovered at the start of the query, or start of first statement,
that had been recovered at the start of the query, or start of first statement
in the case of serializable transactions. In comparison with the primary,
the standby returns query results that could have been obtained on the primary
at some moment in the past.
@ -1103,8 +1103,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</para>
<para>
"Read-only" above means no writes to the permanent database tables.
There are no problems with queries that use transient sort and
"Read-only" above means no writes to the permanent or temporary database
tables. There are no problems with queries that use transient sort and
work files.
</para>
@ -1203,10 +1203,14 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</listitem>
<listitem>
<para>
<command>LOCK TABLE</>, in short default form, since it requests <literal>ACCESS EXCLUSIVE MODE</>.
<command>LOCK TABLE</> that explicitly requests a mode higher than <literal>ROW EXCLUSIVE MODE</>.
</para>
</listitem>
<listitem>
<para>
<command>LOCK TABLE</> in short default form, since it requests <literal>ACCESS EXCLUSIVE MODE</>.
</para>
</listitem>
<listitem>
<para>
Transaction management commands that explicitly set non-read-only state:
@ -1241,7 +1245,7 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</listitem>
<listitem>
<para>
sequence update - nextval()
Sequence update - <function>nextval()</>
</para>
</listitem>
<listitem>
@ -1253,9 +1257,9 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</para>
<para>
Note that the current behaviour of read only transactions when not in
Note that the current behavior of read only transactions when not in
recovery is to allow the last two actions, so there are small and
subtle differences in behaviour between read-only transactions
subtle differences in behavior between read-only transactions
run on a standby and run during normal operation.
It is possible that <command>LISTEN</>, <command>UNLISTEN</>,
<command>NOTIFY</>, and temporary tables might be allowed in a
@ -1275,7 +1279,7 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
issuing <command>SHOW transaction_read_only</>. In addition, a set of
functions (<xref linkend="functions-recovery-info-table">) allow users to
access information about the standby server. These allow you to write
functions that are aware of the current state of the database. These
programs that are aware of the current state of the database. These
can be used to monitor the progress of recovery, or to allow you to
write complex programs that restore the database to particular states.
</para>
@ -1338,7 +1342,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</listitem>
<listitem>
<para>
Waiting to acquire buffer cleanup locks
The standby waiting longer than <varname>max_standby_delay</>
to acquire a buffer cleanup lock.
</para>
</listitem>
<listitem>
@ -1350,27 +1355,28 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
</para>
<para>
Some WAL redo actions will be for <acronym>DDL</> actions. These DDL actions are
repeating actions that have already committed on the primary node, so
they must not fail on the standby node. These DDL locks take priority
and will automatically *cancel* any read-only transactions that get in
their way, after a grace period. This is similar to the possibility of
being canceled by the deadlock detector, but in this case the standby
process always wins, since the replayed actions must not fail. This
also ensures that replication does not fall behind while waiting for a
query to complete. Again, the assumption is that the standby is
primarily for high availability.
Some WAL redo actions will be for <acronym>DDL</> execution. These DDL
actions are replaying changes that have already committed on the primary
node, so they must not fail on the standby node. These DDL locks take
priority and will automatically *cancel* any read-only transactions that
get in their way, after a grace period. This is similar to the possibility
of being canceled by the deadlock detector. But in this case, the standby
recovery process always wins, since the replayed actions must not fail.
This also ensures that replication does not fall behind while waiting for a
query to complete. This prioritization presumes that the standby exists
primarily for high availability, and that adjusting the grace period
will allow a sufficient guard against unexpected cancellation.
</para>
<para>
An example of the above would be an Administrator on Primary server
An example of the above would be an administrator on the primary server
running <command>DROP TABLE</> on a table that is currently being queried
on the standby server.
Clearly the query cannot continue if <command>DROP TABLE</>
proceeds. If this situation occurred on the primary, the <command>DROP TABLE</>
would wait until the query had finished. When <command>DROP TABLE</> is
run on the primary, the primary doesn't have
information about which queries are running on the standby and so
information about which queries are running on the standby, so it
cannot wait for any of the standby queries. The WAL change records come through to the
standby while the standby query is still running, causing a conflict.
</para>
@ -1407,8 +1413,8 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
<para>
If the conflict is caused by a lock, the conflicting standby
transaction is cancelled immediately. If the transaction is
idle-in-transaction then the session is aborted
instead, though this might change in the future.
idle-in-transaction, then the session is aborted instead.
This behavior might change in the future.
</para>
</listitem>
@ -1456,12 +1462,13 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
for as long as needed to run queries on the standby. This guarantees that
a WAL cleanup record is never generated and query conflicts do not occur,
as described above. This could be done using <filename>contrib/dblink</>
and <function>pg_sleep()</>, or via other mechanisms. If you do this, you should note
that this will delay cleanup of dead rows by vacuum or HOT and
people might find this undesirable. However, remember that the
primary and standby nodes are linked via the WAL, so this situation is no
different from the case where the query ran on the primary node itself
except for the benefit of off-loading the execution onto the standby.
and <function>pg_sleep()</>, or via other mechanisms. If you do this, you
should note that this will delay cleanup of dead rows on the primary by
vacuum or HOT, and people might find this undesirable. However, remember
that the primary and standby nodes are linked via the WAL, so the cleanup
situation is no different from the case where the query ran on the primary
node itself. And you are still getting the benefit of off-loading the
execution onto the standby.
</para>
<para>
@ -1494,8 +1501,10 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
be disabled via <filename>postgresql.conf</>. The server might take
some time to enable recovery connections since the server must first complete
sufficient recovery to provide a consistent state against which queries
can run before enabling read only connections. Look for these messages
in the server logs:
can run before enabling read only connections. During this period,
clients that attempt to connect will be refused with an error message.
To confirm the server has come up, either loop retrying to connect from
the application, or look for these messages in the server logs:
<programlisting>
LOG: entering standby mode
@ -1617,9 +1626,9 @@ LOG: database system is ready to accept read only connections
<para>
As a result, you cannot create additional indexes that exist solely
on the standby, nor can statistics exist solely on the standby.
If these administration commands are needed they should be executed
on the primary so that the changes will propagate to the
on the standby, nor statistics that exist solely on the standby.
If these administration commands are needed, they should be executed
on the primary, and eventually those changes will propagate to the
standby.
</para>
@ -1646,12 +1655,12 @@ LOG: database system is ready to accept read only connections
<para>
The <productname>Nagios</> plugin <productname>check_pgsql</> will
work, but it is very simple.
<productname>check_postgres</> will also work, though some actions
could give different or confusing results.
work, because the simple information it checks for exists.
The <productname>check_postgres</> monitoring script will also work,
though some reported values could give different or confusing results.
For example, last vacuum time will not be maintained, since no
vacuum occurs on the standby (though vacuums running on the primary do
send their changes to the standby).
vacuum occurs on the standby. Vacuums running on the primary
do still send their changes to the standby.
</para>
<para>
@ -1715,7 +1724,7 @@ LOG: database system is ready to accept read only connections
In normal (non-recovery) mode, if you issue <command>DROP USER</> or <command>DROP ROLE</>
for a role with login capability while that user is still connected then
nothing happens to the connected user - they remain connected. The user cannot
reconnect however. This behaviour applies in recovery also, so a
reconnect however. This behavior applies in recovery also, so a
<command>DROP USER</> on the primary does not disconnect that user on the standby.
</para>
@ -1729,15 +1738,15 @@ LOG: database system is ready to accept read only connections
</para>
<para>
Autovacuum is not active during recovery, though it will start normally
at the end of recovery.
Autovacuum is not active during recovery, it will start normally at the
end of recovery.
</para>
<para>
The background writer is active during recovery and will perform
restartpoints (similar to checkpoints on the primary) and normal block
cleaning activities. (Remember, hint bits will cause blocks to
be modified on the standby server.)
cleaning activities. This can include updates of the hint bit
information stored on the standby server.
The <command>CHECKPOINT</> command is accepted during recovery,
though it performs a restartpoint rather than a new checkpoint.
</para>
@ -1792,11 +1801,15 @@ LOG: database system is ready to accept read only connections
<para>
Valid starting points for recovery connections are generated at each
checkpoint on the master. If the standby is shut down while the master
is in a shutdown state it might not be possible to re-enter Hot Standby
until the primary is started up so that it generates further starting
points in the WAL logs. This is not considered a serious issue
because the standby is usually switched to act as primary when
the first node is taken down.
is in a shutdown state, it might not be possible to re-enter Hot Standby
until the primary is started up, so that it generates further starting
points in the WAL logs. This situation isn't a problem in the most
common situations where it might happen. Generally, if the primary is
shut down and not available anymore, that's likely due to a serious
failure that requires the standby being converted to operate as
the new primary anyway. And in situations where the primary is
being intentionally taken down, coordinating to make sure the standby
becomes the new primary smoothly is also standard procedure.
</para>
</listitem>
<listitem>

4
doc/src/sgml/installation.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/installation.sgml,v 1.341 2010/02/03 17:25:05 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/installation.sgml,v 1.342 2010/02/19 00:15:25 momjian Exp $ -->
<chapter id="installation">
<title><![%standalone-include[<productname>PostgreSQL</>]]>
@ -2237,7 +2237,7 @@ kill `cat /usr/local/pgsql/data/postmaster.pid`
When implementing PostgreSQL version 8.1 on AIX 5.3, we
periodically ran into problems where the statistics collector
would <quote>mysteriously</quote> not come up successfully. This
appears to be the result of unexpected behaviour in the IPv6
appears to be the result of unexpected behavior in the IPv6
implementation. It looks like PostgreSQL and IPv6 do not play
very well together at this time on AIX.
</para>

2
doc/src/sgml/unaccent.sgml
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@ -9,7 +9,7 @@
<filename>unaccent</> removes accents (diacritic signs) from a lexeme.
It's a filtering dictionary, that means its output is
always passed to the next dictionary (if any), contrary to the standard
behaviour. Currently, it supports most important accents from european
behavior. Currently, it supports most important accents from european
languages.
</para>