database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-30 11:03:19 +03:00
Code Activity

Change ANALYZE to take ShareUpdateExclusiveLock not AccessShareLock on

Browse Source 
the table being analyzed.  This prevents two ANALYZEs from running
concurrently on the same table and possibly suffering concurrent-update
failures while trying to store their results into pg_statistic.  The
downside is that a database-wide ANALYZE executed within a transaction
block will hold ShareUpdateExclusiveLock on many tables simultaneously,
which could lead to concurrency issues or even deadlock against another
such ANALYZE.  However, this seems a corner case of less importance
than getting unexpected errors from a foreground ANALYZE when autovacuum
elects to analyze the same table concurrently.  Per discussion.
This commit is contained in:
Tom Lane
2006-09-17 22:50:31 +00:00
parent 2e5e856f6b
commit da7540b9d1
2 changed files with 193 additions and 194 deletions
Download Patch File Download Diff File Expand all files Collapse all files

349
doc/src/sgml/mvcc.sgml
View File

@ -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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>