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Postgres FD Implementation
Commit da7540b9 authored by Tom Lane's avatar Tom Lane
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Change ANALYZE to take ShareUpdateExclusiveLock not AccessShareLock on 

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.
parent 2e5e856f
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doc/src/sgml/mvcc.sgml
View file @ da7540b9
<!-- $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"> <chapter id="mvcc">
<title>Concurrency Control</title> <title>Concurrency Control</title>
...@@ -77,7 +77,7 @@ ...@@ -77,7 +77,7 @@
</term> </term>
<listitem> <listitem>
<para> <para>
A transaction reads data written by a concurrent uncommitted transaction. A transaction reads data written by a concurrent uncommitted transaction.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -89,9 +89,9 @@ ...@@ -89,9 +89,9 @@
</term> </term>
<listitem> <listitem>
<para> <para>
A transaction re-reads data it has previously read and finds that data A transaction re-reads data it has previously read and finds that data
has been modified by another transaction (that committed since the has been modified by another transaction (that committed since the
initial read). initial read).
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -103,9 +103,9 @@ ...@@ -103,9 +103,9 @@
</term> </term>
<listitem> <listitem>
<para> <para>
A transaction re-executes a query returning a set of rows that satisfy a 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 search condition and finds that the set of rows satisfying the condition
has changed due to another recently-committed transaction. has changed due to another recently-committed transaction.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -125,79 +125,79 @@ ...@@ -125,79 +125,79 @@
<tgroup cols="4"> <tgroup cols="4">
<thead> <thead>
<row> <row>
<entry> <entry>
Isolation Level Isolation Level
</entry> </entry>
<entry> <entry>
Dirty Read Dirty Read
</entry> </entry>
<entry> <entry>
Nonrepeatable Read Nonrepeatable Read
</entry> </entry>
<entry> <entry>
Phantom Read Phantom Read
</entry> </entry>
</row> </row>
</thead> </thead>
<tbody> <tbody>
<row> <row>
<entry> <entry>
Read uncommitted Read uncommitted
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
</row> </row>
<row> <row>
<entry> <entry>
Read committed Read committed
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
</row> </row>
<row> <row>
<entry> <entry>
Repeatable read Repeatable read
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
<entry> <entry>
Possible Possible
</entry> </entry>
</row> </row>
<row> <row>
<entry> <entry>
Serializable Serializable
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
<entry> <entry>
Not possible Not possible
</entry> </entry>
</row> </row>
</tbody> </tbody>
</tgroup> </tgroup>
...@@ -547,174 +547,173 @@ SELECT SUM(value) FROM mytab WHERE class = 2; ...@@ -547,174 +547,173 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
<title>Table-level lock modes</title> <title>Table-level lock modes</title>
<varlistentry> <varlistentry>
<term> <term>
<literal>ACCESS SHARE</literal> <literal>ACCESS SHARE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>ACCESS EXCLUSIVE</literal> lock Conflicts with the <literal>ACCESS EXCLUSIVE</literal> lock
mode only. mode only.
</para> </para>
<para> <para>
The commands <command>SELECT</command> and The <command>SELECT</command> command acquires a lock of this mode on
<command>ANALYZE</command> acquire a lock of this mode on referenced tables. In general, any query that only reads a table
referenced tables. In general, any query that only reads a table and does not modify it will acquire this lock mode.
and does not modify it will acquire this lock mode. </para>
</para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>ROW SHARE</literal> <literal>ROW SHARE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>EXCLUSIVE</literal> and Conflicts with the <literal>EXCLUSIVE</literal> and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
</para> </para>
<para> <para>
The <command>SELECT FOR UPDATE</command> and The <command>SELECT FOR UPDATE</command> and
<command>SELECT FOR SHARE</command> commands acquire a <command>SELECT FOR SHARE</command> commands acquire a
lock of this mode on the target table(s) (in addition to lock of this mode on the target table(s) (in addition to
<literal>ACCESS SHARE</literal> locks on any other tables <literal>ACCESS SHARE</literal> locks on any other tables
that are referenced but not selected that are referenced but not selected
<option>FOR UPDATE/FOR SHARE</option>). <option>FOR UPDATE/FOR SHARE</option>).
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>ROW EXCLUSIVE</literal> <literal>ROW EXCLUSIVE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>SHARE</literal>, <literal>SHARE ROW Conflicts with the <literal>SHARE</literal>, <literal>SHARE ROW
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
</para> </para>
<para> <para>
The commands <command>UPDATE</command>, The commands <command>UPDATE</command>,
<command>DELETE</command>, and <command>INSERT</command> <command>DELETE</command>, and <command>INSERT</command>
acquire this lock mode on the target table (in addition to acquire this lock mode on the target table (in addition to
<literal>ACCESS SHARE</literal> locks on any other referenced <literal>ACCESS SHARE</literal> locks on any other referenced
tables). In general, this lock mode will be acquired by any tables). In general, this lock mode will be acquired by any
command that modifies the data in a table. command that modifies the data in a table.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>SHARE UPDATE EXCLUSIVE</literal> <literal>SHARE UPDATE EXCLUSIVE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>, Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>,
<literal>SHARE</literal>, <literal>SHARE ROW <literal>SHARE</literal>, <literal>SHARE ROW
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
This mode protects a table against This mode protects a table against
concurrent schema changes and <command>VACUUM</> runs. concurrent schema changes and <command>VACUUM</> runs.
</para> </para>
<para> <para>
Acquired by <command>VACUUM</command> (without <option>FULL</option>) Acquired by <command>VACUUM</command> (without <option>FULL</option>),
and by <command>CREATE INDEX CONCURRENTLY</>. <command>ANALYZE</>, and <command>CREATE INDEX CONCURRENTLY</>.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>SHARE</literal> <literal>SHARE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>ROW EXCLUSIVE</literal>, Conflicts with the <literal>ROW EXCLUSIVE</literal>,
<literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE ROW <literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE ROW
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
This mode protects a table against concurrent data changes. This mode protects a table against concurrent data changes.
</para> </para>
<para> <para>
Acquired by <command>CREATE INDEX</command> Acquired by <command>CREATE INDEX</command>
(without <option>CONCURRENTLY</option>). (without <option>CONCURRENTLY</option>).
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>SHARE ROW EXCLUSIVE</literal> <literal>SHARE ROW EXCLUSIVE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>ROW EXCLUSIVE</literal>, Conflicts with the <literal>ROW EXCLUSIVE</literal>,
<literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE UPDATE EXCLUSIVE</literal>,
<literal>SHARE</literal>, <literal>SHARE ROW <literal>SHARE</literal>, <literal>SHARE ROW
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
</para> </para>
<para> <para>
This lock mode is not automatically acquired by any This lock mode is not automatically acquired by any
<productname>PostgreSQL</productname> command. <productname>PostgreSQL</productname> command.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>EXCLUSIVE</literal> <literal>EXCLUSIVE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with the <literal>ROW SHARE</literal>, <literal>ROW Conflicts with the <literal>ROW SHARE</literal>, <literal>ROW
EXCLUSIVE</literal>, <literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE UPDATE
EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE
ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal> lock modes. <literal>ACCESS EXCLUSIVE</literal> lock modes.
This mode allows only concurrent <literal>ACCESS SHARE</literal> locks, This mode allows only concurrent <literal>ACCESS SHARE</literal> locks,
i.e., only reads from the table can proceed in parallel with a i.e., only reads from the table can proceed in parallel with a
transaction holding this lock mode. transaction holding this lock mode.
</para> </para>
<para> <para>
This lock mode is not automatically acquired on user tables by any This lock mode is not automatically acquired on user tables by any
<productname>PostgreSQL</productname> command. However it is <productname>PostgreSQL</productname> command. However it is
acquired on certain system catalogs in some operations. acquired on certain system catalogs in some operations.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term> <term>
<literal>ACCESS EXCLUSIVE</literal> <literal>ACCESS EXCLUSIVE</literal>
</term> </term>
<listitem> <listitem>
<para> <para>
Conflicts with locks of all modes (<literal>ACCESS Conflicts with locks of all modes (<literal>ACCESS
SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW
EXCLUSIVE</literal>, <literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE UPDATE
EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE
ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
<literal>ACCESS EXCLUSIVE</literal>). <literal>ACCESS EXCLUSIVE</literal>).
This mode guarantees that the This mode guarantees that the
holder is the only transaction accessing the table in any way. holder is the only transaction accessing the table in any way.
</para> </para>
<para> <para>
Acquired by the <command>ALTER TABLE</command>, <command>DROP Acquired by the <command>ALTER TABLE</command>, <command>DROP
TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>, TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>,
<command>CLUSTER</command>, and <command>VACUUM FULL</command> <command>CLUSTER</command>, and <command>VACUUM FULL</command>
commands. This is also the default lock mode for <command>LOCK commands. This is also the default lock mode for <command>LOCK
TABLE</command> statements that do not specify a mode explicitly. TABLE</command> statements that do not specify a mode explicitly.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
</variablelist> </variablelist>
...@@ -994,10 +993,10 @@ UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 22222; ...@@ -994,10 +993,10 @@ UPDATE accounts SET balance = balance - 100.00 WHERE acctnum = 22222;
</term> </term>
<listitem> <listitem>
<para> <para>
Short-term share/exclusive page-level locks are used for Short-term share/exclusive page-level locks are used for
read/write access. Locks are released immediately after each read/write access. Locks are released immediately after each
index row is fetched or inserted. However, note that GIN index index row is fetched or inserted. However, note that a GIN index
usually requires several inserts per one table row. usually requires several inserts for each table row.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
......
src/backend/commands/analyze.c
View file @ da7540b9
...@@ -8,7 +8,7 @@ ...@@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.97 2006/08/18 16:09:08 tgl Exp $ * $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.98 2006/09/17 22:50:31 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
...@@ -129,10 +129,14 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -129,10 +129,14 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
CHECK_FOR_INTERRUPTS(); CHECK_FOR_INTERRUPTS();
/* /*
* Open the relation, getting only a read lock on it. If the rel has * Open the relation, getting ShareUpdateExclusiveLock to ensure that
* been dropped since we last saw it, we don't need to process it. * two ANALYZEs don't run on it concurrently. (This also locks out
* a concurrent VACUUM, which doesn't matter much at the moment but
* might matter if we ever try to accumulate stats on dead tuples.)
* If the rel has been dropped since we last saw it, we don't need
* to process it.
*/ */
onerel = try_relation_open(relid, AccessShareLock); onerel = try_relation_open(relid, ShareUpdateExclusiveLock);
if (!onerel) if (!onerel)
return; return;
...@@ -147,7 +151,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -147,7 +151,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
ereport(WARNING, ereport(WARNING,
(errmsg("skipping \"%s\" --- only table or database owner can analyze it", (errmsg("skipping \"%s\" --- only table or database owner can analyze it",
RelationGetRelationName(onerel)))); RelationGetRelationName(onerel))));
relation_close(onerel, AccessShareLock); relation_close(onerel, ShareUpdateExclusiveLock);
return; return;
} }
...@@ -162,7 +166,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -162,7 +166,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
ereport(WARNING, ereport(WARNING,
(errmsg("skipping \"%s\" --- cannot analyze indexes, views, or special system tables", (errmsg("skipping \"%s\" --- cannot analyze indexes, views, or special system tables",
RelationGetRelationName(onerel)))); RelationGetRelationName(onerel))));
relation_close(onerel, AccessShareLock); relation_close(onerel, ShareUpdateExclusiveLock);
return; return;
} }
...@@ -174,7 +178,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -174,7 +178,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
*/ */
if (isOtherTempNamespace(RelationGetNamespace(onerel))) if (isOtherTempNamespace(RelationGetNamespace(onerel)))
{ {
relation_close(onerel, AccessShareLock); relation_close(onerel, ShareUpdateExclusiveLock);
return; return;
} }
...@@ -183,7 +187,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -183,7 +187,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
*/ */
if (RelationGetRelid(onerel) == StatisticRelationId) if (RelationGetRelid(onerel) == StatisticRelationId)
{ {
relation_close(onerel, AccessShareLock); relation_close(onerel, ShareUpdateExclusiveLock);
return; return;
} }
...@@ -317,7 +321,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -317,7 +321,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
0, 0); 0, 0);
vac_close_indexes(nindexes, Irel, AccessShareLock); vac_close_indexes(nindexes, Irel, AccessShareLock);
relation_close(onerel, AccessShareLock); relation_close(onerel, ShareUpdateExclusiveLock);
return; return;
} }
...@@ -444,7 +448,8 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt) ...@@ -444,7 +448,8 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
/* /*
* Close source relation now, but keep lock so that no one deletes it * Close source relation now, but keep lock so that no one deletes it
* before we commit. (If someone did, they'd fail to clean up the entries * before we commit. (If someone did, they'd fail to clean up the entries
* we made in pg_statistic.) * we made in pg_statistic. Also, releasing the lock before commit would
* expose us to concurrent-update failures in update_attstats.)
*/ */
relation_close(onerel, NoLock); relation_close(onerel, NoLock);
} }
...@@ -1079,14 +1084,9 @@ compare_rows(const void *a, const void *b) ...@@ -1079,14 +1084,9 @@ compare_rows(const void *a, const void *b)
* Note analyze_rel() has seen to it that we won't come here when * Note analyze_rel() has seen to it that we won't come here when
* vacuuming pg_statistic itself. * vacuuming pg_statistic itself.
* *
* Note: if two backends concurrently try to analyze the same relation, * Note: there would be a race condition here if two backends could
* the second one is likely to fail here with a "tuple concurrently * ANALYZE the same table concurrently. Presently, we lock that out
* updated" error. This is slightly annoying, but no real harm is done. * by taking a self-exclusive lock on the relation in analyze_rel().
* We could prevent the problem by using a stronger lock on the
* relation for ANALYZE (ie, ShareUpdateExclusiveLock instead
* of AccessShareLock); but that cure seems worse than the disease,
* especially now that ANALYZE doesn't start a new transaction
* for each relation. The lock could be held for a long time...
*/ */
static void static void
update_attstats(Oid relid, int natts, VacAttrStats **vacattrstats) update_attstats(Oid relid, int natts, VacAttrStats **vacattrstats)
...@@ -1202,7 +1202,7 @@ update_attstats(Oid relid, int natts, VacAttrStats **vacattrstats) ...@@ -1202,7 +1202,7 @@ update_attstats(Oid relid, int natts, VacAttrStats **vacattrstats)
else else
{ {
/* No, insert new tuple */ /* No, insert new tuple */
stup = heap_formtuple(sd->rd_att, values, nulls); stup = heap_formtuple(RelationGetDescr(sd), values, nulls);
simple_heap_insert(sd, stup); simple_heap_insert(sd, stup);
} }
......
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