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simonat2ndQuadrantsimonat2ndQuadrant
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Reduce lock levels of CREATE TRIGGER and some ALTER TABLE, CREATE RULE actions.
Avoid hard-coding lockmode used for many altering DDL commands, allowing easier future changes of lock levels. Implementation of initial analysis on DDL sub-commands, so that many lock levels are now at ShareUpdateExclusiveLock or ShareRowExclusiveLock, allowing certain DDL not to block reads/writes. First of number of planned changes in this area; additional docs required when full project complete.
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10 files changed

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‎doc/src/sgml/mvcc.sgml‎

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@@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.75 2010/05/03 15:35:30 alvherre Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/mvcc.sgml,v 2.76 2010/07/28 05:22:24 sriggs Exp $ -->
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<chapter id="mvcc">
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<title>Concurrency Control</title>
@@ -532,7 +532,7 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
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most <productname>PostgreSQL</productname> commands automatically
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acquire locks of appropriate modes to ensure that referenced
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tables are not dropped or modified in incompatible ways while the
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command executes. (For example, <command>ALTER TABLE</> cannot safely be
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command executes. (For example, <command>TRUNCATE</> cannot safely be
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executed concurrently with other operations on the same table, so it
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obtains an exclusive lock on the table to enforce that.)
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</para>
@@ -695,8 +695,9 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
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</para>
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<para>
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This lock mode is not automatically acquired by any
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<productname>PostgreSQL</productname> command.
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Acquired by <command>CREATE TRIGGER</command>,
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<command>CREATE RULE</command> (except for <literal>ON SELECT</>
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rules) and in some cases <command>ALTER TABLE</command>.
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</para>
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</listitem>
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</varlistentry>
@@ -742,11 +743,12 @@ SELECT SUM(value) FROM mytab WHERE class = 2;
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</para>
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<para>
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Acquired by the <command>ALTER TABLE</command>, <command>DROP
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TABLE</command>, <command>TRUNCATE</command>, <command>REINDEX</command>,
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Acquired by the <command>DROP TABLE</command>,
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<command>TRUNCATE</command>, <command>REINDEX</command>,
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<command>CLUSTER</command>, and <command>VACUUM FULL</command>
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commands. This is also the default lock mode for <command>LOCK
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TABLE</command> statements that do not specify a mode explicitly.
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commands, as well as most variants of <command>ALTER TABLE</>.
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This is also the default lock mode for <command>LOCK TABLE</command>
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statements that do not specify a mode explicitly.
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</para>
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</listitem>
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</varlistentry>

‎src/backend/catalog/pg_shdepend.c‎

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@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/catalog/pg_shdepend.c,v 1.43 2010/07/06 19:18:56 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/catalog/pg_shdepend.c,v 1.44 2010/07/28 05:22:24 sriggs Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -1346,7 +1346,7 @@ shdepReassignOwned(List *roleids, Oid newrole)
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* owned sequences, etc when we happen to visit them
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* before their parent table.
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*/
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ATExecChangeOwner(sdepForm->objid, newrole, true);
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ATExecChangeOwner(sdepForm->objid, newrole, true, AccessExclusiveLock);
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break;
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case ProcedureRelationId:

‎src/backend/commands/alter.c‎

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Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/alter.c,v 1.36 2010/06/13 17:43:12 rhaas Exp $
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* $PostgreSQL: pgsql/src/backend/commands/alter.c,v 1.37 2010/07/28 05:22:24 sriggs Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -190,7 +190,7 @@ ExecAlterObjectSchemaStmt(AlterObjectSchemaStmt *stmt)
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case OBJECT_VIEW:
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CheckRelationOwnership(stmt->relation, true);
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AlterTableNamespace(stmt->relation, stmt->newschema,
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stmt->objectType);
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stmt->objectType, AccessExclusiveLock);
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break;
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case OBJECT_TYPE:

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