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Diffstat (limited to 'doc/src/sgml/mvcc.sgml')
| -rw-r--r-- | doc/src/sgml/mvcc.sgml | 365 |
1 files changed, 182 insertions, 183 deletions
diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml index a9d7a9d5f98..d2deee2bfca 100644 --- a/doc/src/sgml/mvcc.sgml +++ b/doc/src/sgml/mvcc.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.60 2006/09/16 00:30:14 momjian Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.61 2006/09/17 22:50:31 tgl Exp $ --> <chapter id="mvcc"> <title>Concurrency Control</title> @@ -77,7 +77,7 @@ </term> <listitem> <para> - A transaction reads data written by a concurrent uncommitted transaction. + A transaction reads data written by a concurrent uncommitted transaction. </para> </listitem> </varlistentry> @@ -89,9 +89,9 @@ </term> <listitem> <para> - A transaction re-reads data it has previously read and finds that data - has been modified by another transaction (that committed since the - initial read). + A transaction re-reads data it has previously read and finds that data + has been modified by another transaction (that committed since the + initial read). </para> </listitem> </varlistentry> @@ -103,9 +103,9 @@ </term> <listitem> <para> - A transaction re-executes a query returning a set of rows that satisfy a - search condition and finds that the set of rows satisfying the condition - has changed due to another recently-committed transaction. + A transaction re-executes a query returning a set of rows that satisfy a + search condition and finds that the set of rows satisfying the condition + has changed due to another recently-committed transaction. </para> </listitem> </varlistentry> @@ -125,79 +125,79 @@ <tgroup cols="4"> <thead> <row> - <entry> + <entry> Isolation Level - </entry> - <entry> - Dirty Read - </entry> - <entry> - Nonrepeatable Read - </entry> - <entry> - Phantom Read - </entry> + </entry> + <entry> + Dirty Read + </entry> + <entry> + Nonrepeatable Read + </entry> + <entry> + Phantom Read + </entry> </row> </thead> <tbody> <row> - <entry> - Read uncommitted - </entry> - <entry> - Possible - </entry> - <entry> - Possible - </entry> - <entry> - Possible - </entry> + <entry> + Read uncommitted + </entry> + <entry> + Possible + </entry> + <entry> + Possible + </entry> + <entry> + Possible + </entry> </row> <row> - <entry> - Read committed - </entry> - <entry> - Not possible - </entry> - <entry> - Possible - </entry> - <entry> - Possible - </entry> + <entry> + Read committed + </entry> + <entry> + Not possible + </entry> + <entry> + Possible + </entry> + <entry> + Possible + </entry> </row> <row> - <entry> - Repeatable read - </entry> - <entry> - Not possible - </entry> - <entry> - Not possible - </entry> - <entry> - Possible - </entry> + <entry> + Repeatable read + </entry> + <entry> + Not possible + </entry> + <entry> + Not possible + </entry> + <entry> + Possible + </entry> </row> <row> - <entry> - Serializable - </entry> - <entry> - Not possible - </entry> - <entry> - Not possible - </entry> - <entry> - Not possible - </entry> + <entry> + Serializable + </entry> + <entry> + Not possible + </entry> + <entry> + Not possible + </entry> + <entry> + Not possible + </entry> </row> </tbody> </tgroup> @@ -547,174 +547,173 @@ SELECT SUM(value) FROM mytab WHERE class = 2; <title>Table-level lock modes</title> <varlistentry> <term> - <literal>ACCESS SHARE</literal> + <literal>ACCESS SHARE</literal> </term> <listitem> - <para> - Conflicts with the <literal>ACCESS EXCLUSIVE</literal> lock - mode only. - </para> - - <para> - The commands <command>SELECT</command> and - <command>ANALYZE</command> acquire a lock of this mode on - referenced tables. In general, any query that only reads a table - and does not modify it will acquire this lock mode. - </para> + <para> + Conflicts with the <literal>ACCESS EXCLUSIVE</literal> lock + mode only. + </para> + + <para> + The <command>SELECT</command> command acquires a lock of this mode on + referenced tables. In general, any query that only reads a table + and does not modify it will acquire this lock mode. + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>ROW SHARE</literal> + <literal>ROW SHARE</literal> </term> <listitem> - <para> - Conflicts with the <literal>EXCLUSIVE</literal> and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - </para> - - <para> - The <command>SELECT FOR UPDATE</command> and - <command>SELECT FOR SHARE</command> commands acquire a - lock of this mode on the target table(s) (in addition to - <literal>ACCESS SHARE</literal> locks on any other tables - that are referenced but not selected - <option>FOR UPDATE/FOR SHARE</option>). - </para> + <para> + Conflicts with the <literal>EXCLUSIVE</literal> and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + </para> + + <para> + The <command>SELECT FOR UPDATE</command> and + <command>SELECT FOR SHARE</command> commands acquire a + lock of this mode on the target table(s) (in addition to + <literal>ACCESS SHARE</literal> locks on any other tables + that are referenced but not selected + <option>FOR UPDATE/FOR SHARE</option>). + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>ROW EXCLUSIVE</literal> + <literal>ROW EXCLUSIVE</literal> </term> <listitem> - <para> - Conflicts with the <literal>SHARE</literal>, <literal>SHARE ROW - EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - </para> - - <para> - The commands <command>UPDATE</command>, - <command>DELETE</command>, and <command>INSERT</command> - acquire this lock mode on the target table (in addition to - <literal>ACCESS SHARE</literal> locks on any other referenced - tables). In general, this lock mode will be acquired by any - command that modifies the data in a table. - </para> + <para> + Conflicts with the <literal>SHARE</literal>, <literal>SHARE ROW + EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + </para> + + <para> + The commands <command>UPDATE</command>, + <command>DELETE</command>, and <command>INSERT</command> + acquire this lock mode on the target table (in addition to + <literal>ACCESS SHARE</literal> locks on any other referenced + tables). In general, this lock mode will be acquired by any + command that modifies the data in a table. + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>SHARE UPDATE EXCLUSIVE</literal> + <literal>SHARE UPDATE EXCLUSIVE</literal> </term> <listitem> - <para> - Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>, - <literal>SHARE</literal>, <literal>SHARE ROW - EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - This mode protects a table against - concurrent schema changes and <command>VACUUM</> runs. - </para> - - <para> - Acquired by <command>VACUUM</command> (without <option>FULL</option>) - and by <command>CREATE INDEX CONCURRENTLY</>. - </para> + <para> + Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>, + <literal>SHARE</literal>, <literal>SHARE ROW + EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + This mode protects a table against + concurrent schema changes and <command>VACUUM</> runs. + </para> + + <para> + Acquired by <command>VACUUM</command> (without <option>FULL</option>), + <command>ANALYZE</>, and <command>CREATE INDEX CONCURRENTLY</>. + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>SHARE</literal> + <literal>SHARE</literal> </term> <listitem> - <para> - Conflicts with the <literal>ROW EXCLUSIVE</literal>, - <literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE ROW - EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - This mode protects a table against concurrent data changes. - </para> - - <para> - Acquired by <command>CREATE INDEX</command> - (without <option>CONCURRENTLY</option>). - </para> + <para> + Conflicts with the <literal>ROW EXCLUSIVE</literal>, + <literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE ROW + EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + This mode protects a table against concurrent data changes. + </para> + + <para> + Acquired by <command>CREATE INDEX</command> + (without <option>CONCURRENTLY</option>). + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>SHARE ROW EXCLUSIVE</literal> + <literal>SHARE ROW EXCLUSIVE</literal> </term> <listitem> - <para> - Conflicts with the <literal>ROW EXCLUSIVE</literal>, - <literal>SHARE UPDATE EXCLUSIVE</literal>, - <literal>SHARE</literal>, <literal>SHARE ROW - EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - </para> - - <para> + <para> + Conflicts with the <literal>ROW EXCLUSIVE</literal>, + <literal>SHARE UPDATE EXCLUSIVE</literal>, + <literal>SHARE</literal>, <literal>SHARE ROW + EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + </para> + + <para> This lock mode is not automatically acquired by any <productname>PostgreSQL</productname> command. - </para> + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>EXCLUSIVE</literal> + <literal>EXCLUSIVE</literal> </term> <listitem> - <para> - Conflicts with the <literal>ROW SHARE</literal>, <literal>ROW - EXCLUSIVE</literal>, <literal>SHARE UPDATE - EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE - ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal> lock modes. - This mode allows only concurrent <literal>ACCESS SHARE</literal> locks, - i.e., only reads from the table can proceed in parallel with a - transaction holding this lock mode. - </para> - - <para> + <para> + Conflicts with the <literal>ROW SHARE</literal>, <literal>ROW + EXCLUSIVE</literal>, <literal>SHARE UPDATE + EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE + ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal> lock modes. + This mode allows only concurrent <literal>ACCESS SHARE</literal> locks, + i.e., only reads from the table can proceed in parallel with a + transaction holding this lock mode. + </para> + + <para> This lock mode is not automatically acquired on user tables by any <productname>PostgreSQL</productname> command. However it is acquired on certain system catalogs in some operations. - </para> + </para> </listitem> </varlistentry> <varlistentry> <term> - <literal>ACCESS EXCLUSIVE</literal> + <literal>ACCESS EXCLUSIVE</literal> </term> <listitem> - <para> - Conflicts with locks of all modes (<literal>ACCESS - SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW - EXCLUSIVE</literal>, <literal>SHARE UPDATE - EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE - ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and - <literal>ACCESS EXCLUSIVE</literal>). - This mode guarantees that the - holder is the only transaction accessing the table in any way. - </para> - - <para> - Acquired by the <command>ALTER TABLE</command>, <command>DROP - TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>, - <command>CLUSTER</command>, and <command>VACUUM FULL</command> - commands. This is also the default lock mode for <command>LOCK - TABLE</command> statements that do not specify a mode explicitly. - </para> + <para> + Conflicts with locks of all modes (<literal>ACCESS + SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW + EXCLUSIVE</literal>, <literal>SHARE UPDATE + EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE + ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and + <literal>ACCESS EXCLUSIVE</literal>). + This mode guarantees that the + holder is the only transaction accessing the table in any way. + </para> + + <para> + Acquired by the <command>ALTER TABLE</command>, <command>DROP + TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>, + <command>CLUSTER</command>, and <command>VACUUM FULL</command> + commands. This is also the default lock mode for <command>LOCK + TABLE</command> statements that do not specify a mode explicitly. + </para> </listitem> </varlistentry> </variablelist> @@ -994,10 +993,10 @@ UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 22222; </term> <listitem> <para> - Short-term share/exclusive page-level locks are used for - read/write access. Locks are released immediately after each - index row is fetched or inserted. However, note that GIN index - usually requires several inserts per one table row. + Short-term share/exclusive page-level locks are used for + read/write access. Locks are released immediately after each + index row is fetched or inserted. However, note that a GIN index + usually requires several inserts for each table row. </para> </listitem> </varlistentry> |