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Add transaction-level advisory locks.

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They share the same locking namespace with the existing session-level
advisory locks, but they are automatically released at the end of the
current transaction and cannot be released explicitly via unlock
functions.

Marko Tiikkaja, reviewed by me.
This commit is contained in:
Itagaki Takahiro
2011-02-18 14:04:34 +09:00
parent 87bb2ade2c
commit 62c7bd31c8
14 changed files with 814 additions and 71 deletions
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128
doc/src/sgml/func.sgml
View File

@ -14623,91 +14623,147 @@ SELECT (pg_stat_file('filename')).modification;
<literal><function>pg_advisory_lock(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain exclusive advisory lock</entry>
<entry>Obtain exclusive session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_lock(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain exclusive advisory lock</entry>
<entry>Obtain exclusive session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_lock_shared(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain shared advisory lock</entry>
<entry>Obtain shared session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_lock_shared(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain shared advisory lock</entry>
<entry>Obtain shared session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_unlock(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Release an exclusive advisory lock</entry>
<entry>Release an exclusive session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_unlock(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Release an exclusive advisory lock</entry>
<entry>Release an exclusive session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_unlock_all()</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Release all advisory locks held by the current session</entry>
<entry>Release all session level advisory locks held by the current session</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_unlock_shared(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Release a shared advisory lock</entry>
<entry>Release a shared session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_unlock_shared(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Release a shared advisory lock</entry>
<entry>Release a shared session level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_xact_lock(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain exclusive transaction level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_xact_lock(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain exclusive transaction level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_xact_lock_shared(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain shared transaction level advisory lock</entry>
</row>
<row>
<entry>
<literal><function>pg_advisory_xact_lock_shared(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>void</type></entry>
<entry>Obtain shared advisory lock for the current transaction</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_lock(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain exclusive advisory lock if available</entry>
<entry>Obtain exclusive session level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_lock(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain exclusive advisory lock if available</entry>
<entry>Obtain exclusive session level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_lock_shared(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain shared advisory lock if available</entry>
<entry>Obtain shared session level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_lock_shared(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain shared advisory lock if available</entry>
<entry>Obtain shared session level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_xact_lock(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain exclusive transaction level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_xact_lock(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain exclusive transaction level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_xact_lock_shared(<parameter>key</> <type>bigint</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain shared transaction level advisory lock if available</entry>
</row>
<row>
<entry>
<literal><function>pg_try_advisory_xact_lock_shared(<parameter>key1</> <type>int</>, <parameter>key2</> <type>int</>)</function></literal>
</entry>
<entry><type>boolean</type></entry>
<entry>Obtain shared transaction level advisory lock if available</entry>
</row>
</tbody>
</tgroup>
@ -14758,12 +14814,50 @@ SELECT (pg_stat_file('filename')).modification;
a shared rather than an exclusive lock.
</para>
<indexterm>
<primary>pg_advisory_xact_lock</primary>
</indexterm>
<para>
<function>pg_advisory_xact_lock</> works the same as
<function>pg_advisory_lock</>, expect the lock is automatically released
at the end of the current transaction and can not be released explicitly.
</para>
<indexterm>
<primary>pg_advisory_xact_lock_shared</primary>
</indexterm>
<para>
<function>pg_advisory_xact_lock_shared</> works the same as
<function>pg_advisory_lock_shared</>, expect the lock is automatically released
at the end of the current transaction and can not be released explicitly.
</para>
<indexterm>
<primary>pg_try_advisory_xact_lock</primary>
</indexterm>
<para>
<function>pg_try_advisory_xact_lock</> works the same as
<function>pg_try_advisory_lock</>, expect the lock, if acquired,
is automatically released at the end of the current transaction and
can not be released explicitly.
</para>
<indexterm>
<primary>pg_try_advisory_xact_lock_shared</primary>
</indexterm>
<para>
<function>pg_try_advisory_xact_lock_shared</> works the same as
<function>pg_try_advisory_lock_shared</>, expect the lock, if acquired,
is automatically released at the end of the current transaction and
can not be released explicitly.
</para>
<indexterm>
<primary>pg_advisory_unlock</primary>
</indexterm>
<para>
<function>pg_advisory_unlock</> will release a previously-acquired
exclusive advisory lock. It
exclusive session level advisory lock. It
returns <literal>true</> if the lock is successfully released.
If the lock was not held, it will return <literal>false</>,
and in addition, an SQL warning will be raised by the server.
@ -14775,15 +14869,15 @@ SELECT (pg_stat_file('filename')).modification;
<para>
<function>pg_advisory_unlock_shared</> works the same as
<function>pg_advisory_unlock</>,
except it releases a shared advisory lock.
except it releases a shared session level advisory lock.
</para>
<indexterm>
<primary>pg_advisory_unlock_all</primary>
</indexterm>
<para>
<function>pg_advisory_unlock_all</> will release all advisory locks
held by the current session. (This function is implicitly invoked
<function>pg_advisory_unlock_all</> will release all session level advisory
locks held by the current session. (This function is implicitly invoked
at session end, even if the client disconnects ungracefully.)
</para>

35
doc/src/sgml/mvcc.sgml
View File

@ -1199,19 +1199,28 @@ UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 22222;
called <firstterm>advisory locks</>, because the system does not
enforce their use &mdash; it is up to the application to use them
correctly. Advisory locks can be useful for locking strategies
that are an awkward fit for the MVCC model. Once acquired, an
advisory lock is held until explicitly released or the session ends.
Unlike standard locks, advisory locks do not
honor transaction semantics: a lock acquired during a
transaction that is later rolled back will still be held following the
that are an awkward fit for the MVCC model.</para>
<para>
There are two different types of advisory locks in
<productname>PostgreSQL</productname>: session level and transaction level.
Once acquired, a session level advisory lock is held until explicitly
released or the session ends. Unlike standard locks, session level
advisory locks do not honor transaction semantics: a lock acquired during
a transaction that is later rolled back will still be held following the
rollback, and likewise an unlock is effective even if the calling
transaction fails later. The same lock can be acquired multiple times by
its owning process: for each lock request there must be a corresponding
unlock request before the lock is actually released. (If a session
already holds a given lock, additional requests will always succeed, even
if other sessions are awaiting the lock.) Like all locks in
<productname>PostgreSQL</productname>, a complete list of advisory
locks currently held by any session can be found in the
transaction fails later. The same session level lock can be acquired
multiple times by its owning process: for each lock request there must be
a corresponding unlock request before the lock is actually released. (If a
session already holds a given lock, additional requests will always succeed,
even if other sessions are awaiting the lock.) Transaction level locks on
the other hand behave more like regular locks; they are automatically
released at the end of the transaction, and can not be explicitly unlocked.
Session and transaction level locks share the same lock space, which means
that a transaction level lock will prevent another session from obtaining
a session level lock on that same resource and vice versa.
Like all locks in <productname>PostgreSQL</productname>, a complete list of
advisory locks currently held by any session can be found in the
<link linkend="view-pg-locks"><structname>pg_locks</structname></link>
system view.
</para>
@ -1233,7 +1242,7 @@ UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 22222;
strategies typical of so called <quote>flat file</> data management
systems.
While a flag stored in a table could be used for the same purpose,
advisory locks are faster, avoid MVCC bloat, and are automatically
advisory locks are faster, avoid MVCC bloat, and can be automatically
cleaned up by the server at the end of the session.
In certain cases using this advisory locking method, especially in queries
involving explicit ordering and <literal>LIMIT</> clauses, care must be