Re: Implementing SELECT FOR UPDATE [NOWAIT]

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От Bruce Momjian
Тема Re: Implementing SELECT FOR UPDATE [NOWAIT]
Дата
Msg-id 200506101601.j5AG12329341@candle.pha.pa.us
обсуждение исходный текст
Ответ на Implementing SELECT FOR UPDATE [NOWAIT]  (Hans-Juergen Schoenig <hs@cybertec.at>)
Ответы Re: Implementing SELECT FOR UPDATE [NOWAIT]  (Bruce Momjian <pgman@candle.pha.pa.us>)
Список pgsql-patches
Uh, seems the code has drifted too much and now I can't apply this.
Would you redo this against current CVS?  Thanks.

---------------------------------------------------------------------------

Hans-Juergen Schoenig wrote:
> Folks,
>
> We have implemented SELECT FOR UPDATE NOWAIT for PostgreSQL.
> The patch attached to this email contains all the required code
> including ECPG updates and some documentation.
> It would be nice if this patch would be included in PostgreSQL 8.1
>
>     Best regards,
>
>         Ewald Geschwinde & Hans-Juergen Schoenig
>
> --
> Cybertec Geschwinde u Schoenig GmbH.
> Schoengrabern 134, A-2020 Hollabrunn, Austria
> Tel: +43/660/816 40 77
> www.cybertec.at, www.postgresql.at

[ text/x-patch is unsupported, treating like TEXT/PLAIN ]

> diff -r -c postgresql-8.0.0rc2.orig/doc/src/sgml/ref/select.sgml postgresql-8.0.0rc2/doc/src/sgml/ref/select.sgml
> *** postgresql-8.0.0rc2.orig/doc/src/sgml/ref/select.sgml    Sat Nov 27 22:27:07 2004
> --- postgresql-8.0.0rc2/doc/src/sgml/ref/select.sgml    Mon Dec 27 10:57:05 2004
> ***************
> *** 30,36 ****
>       [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable
class="parameter">operator</replaceable>] [, ...] ] 
>       [ LIMIT { <replaceable class="parameter">count</replaceable> | ALL } ]
>       [ OFFSET <replaceable class="parameter">start</replaceable> ]
> !     [ FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] ]
>
>   where <replaceable class="parameter">from_item</replaceable> can be one of:
>
> --- 30,36 ----
>       [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable
class="parameter">operator</replaceable>] [, ...] ] 
>       [ LIMIT { <replaceable class="parameter">count</replaceable> | ALL } ]
>       [ OFFSET <replaceable class="parameter">start</replaceable> ]
> !     [ FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [NOWAIT] ]
>
>   where <replaceable class="parameter">from_item</replaceable> can be one of:
>
> ***************
> *** 772,778 ****
>      <para>
>       The <literal>FOR UPDATE</literal> clause has this form:
>   <synopsis>
> ! FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ]
>   </synopsis>
>      </para>
>
> --- 772,778 ----
>      <para>
>       The <literal>FOR UPDATE</literal> clause has this form:
>   <synopsis>
> ! FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [NOWAIT]
>   </synopsis>
>      </para>
>
> ***************
> *** 789,796 ****
>       has already locked a selected row or rows, <command>SELECT FOR
>       UPDATE</command> will wait for the other transaction to complete,
>       and will then lock and return the updated row (or no row, if the
> !     row was deleted).  For further discussion see <xref
> !     linkend="mvcc">.
>      </para>
>
>      <para>
> --- 789,802 ----
>       has already locked a selected row or rows, <command>SELECT FOR
>       UPDATE</command> will wait for the other transaction to complete,
>       and will then lock and return the updated row (or no row, if the
> !     row was deleted).  If the current transaction is not supposed to
> !     wait on other transactions to commit the NOWAIT option can be
> !     used.  If <command>SELECT FOR UPDATE NOWAIT</command> finds out
> !     that somebody else is holding a lock an error will be thrown.
> !     This will only happen in case of row level locks - if somebody
> !     holds a table lock <command>SELECT FOR UPDATE NOWAIT</command>
> !     will still wait for concurrent transactions.  For further
> !     discussion see <xref linkend="mvcc">.
>      </para>
>
>      <para>
> diff -r -c postgresql-8.0.0rc2.orig/doc/src/sgml/sql.sgml postgresql-8.0.0rc2/doc/src/sgml/sql.sgml
> *** postgresql-8.0.0rc2.orig/doc/src/sgml/sql.sgml    Mon Nov 15 07:32:14 2004
> --- postgresql-8.0.0rc2/doc/src/sgml/sql.sgml    Mon Dec 27 10:57:05 2004
> ***************
> *** 866,872 ****
>       [ ORDER BY <replaceable class="PARAMETER">expression</replaceable> [ ASC | DESC | USING <replaceable
class="PARAMETER">operator</replaceable>] [, ...] ] 
>       [ LIMIT { <replaceable class="PARAMETER">count</replaceable> | ALL } ]
>       [ OFFSET <replaceable class="PARAMETER">start</replaceable> ]
> !     [ FOR UPDATE [ OF <replaceable class="PARAMETER">class_name</replaceable> [, ...] ] ]
>        </synopsis>
>       </para>
>
> --- 866,872 ----
>       [ ORDER BY <replaceable class="PARAMETER">expression</replaceable> [ ASC | DESC | USING <replaceable
class="PARAMETER">operator</replaceable>] [, ...] ] 
>       [ LIMIT { <replaceable class="PARAMETER">count</replaceable> | ALL } ]
>       [ OFFSET <replaceable class="PARAMETER">start</replaceable> ]
> !     [ FOR UPDATE [ OF <replaceable class="PARAMETER">class_name</replaceable> [, ...] ] [NOWAIT] ]
>        </synopsis>
>       </para>
>
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/access/heap/heapam.c
postgresql-8.0.0rc2/src/backend/access/heap/heapam.c
> *** postgresql-8.0.0rc2.orig/src/backend/access/heap/heapam.c    Sun Nov 14 03:04:12 2004
> --- postgresql-8.0.0rc2/src/backend/access/heap/heapam.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 16,21 ****
> --- 16,22 ----
>    *        relation_openrv - open any relation specified by a RangeVar
>    *        relation_openr    - open a system relation by name
>    *        relation_close    - close any relation
> +  *        conditional_relation_open - open with option not to wait
>    *        heap_open        - open a heap relation by relation OID
>    *        heap_openrv        - open a heap relation specified by a RangeVar
>    *        heap_openr        - open a system heap relation by name
> ***************
> *** 1828,1834 ****
>    */
>   int
>   heap_mark4update(Relation relation, HeapTuple tuple, Buffer *buffer,
> !                  CommandId cid)
>   {
>       TransactionId xid = GetCurrentTransactionId();
>       ItemPointer tid = &(tuple->t_self);
> --- 1829,1835 ----
>    */
>   int
>   heap_mark4update(Relation relation, HeapTuple tuple, Buffer *buffer,
> !                  CommandId cid, bool nowait)
>   {
>       TransactionId xid = GetCurrentTransactionId();
>       ItemPointer tid = &(tuple->t_self);
> ***************
> *** 1858,1866 ****
>       {
>           TransactionId xwait = HeapTupleHeaderGetXmax(tuple->t_data);
>
> -         /* sleep until concurrent transaction ends */
>           LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
> !         XactLockTableWait(xwait);
>
>           LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
>           if (!TransactionIdDidCommit(xwait))
> --- 1859,1881 ----
>       {
>           TransactionId xwait = HeapTupleHeaderGetXmax(tuple->t_data);
>
>           LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
> !
> !         if (nowait)
> !         {
> !             /* rather error than sleep until concurrent transaction ends */
> !             if (!ConditionalXactLockTableWait(xwait))
> !             {
> !                 ReleaseBuffer(*buffer);
> !                 ereport(ERROR,
> !                     (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> !                      errmsg("data in table \"%s\" was modify by concurrent trasaction.",
> !                          RelationGetRelationName(relation))));
> !             }
> !         }
> !         else
> !             /* sleep until concurrent transaction ends */
> !             XactLockTableWait(xwait);
>
>           LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
>           if (!TransactionIdDidCommit(xwait))
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/commands/trigger.c postgresql-8.0.0rc2/src/backend/commands/trigger.c
> *** postgresql-8.0.0rc2.orig/src/backend/commands/trigger.c    Tue Dec  7 00:57:17 2004
> --- postgresql-8.0.0rc2/src/backend/commands/trigger.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 1574,1580 ****
>           *newSlot = NULL;
>           tuple.t_self = *tid;
>   ltrmark:;
> !         test = heap_mark4update(relation, &tuple, &buffer, cid);
>           switch (test)
>           {
>               case HeapTupleSelfUpdated:
> --- 1574,1580 ----
>           *newSlot = NULL;
>           tuple.t_self = *tid;
>   ltrmark:;
> !         test = heap_mark4update(relation, &tuple, &buffer, cid, estate->es_nowait);
>           switch (test)
>           {
>               case HeapTupleSelfUpdated:
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/executor/execMain.c
postgresql-8.0.0rc2/src/backend/executor/execMain.c
> *** postgresql-8.0.0rc2.orig/src/backend/executor/execMain.c    Thu Oct  7 20:38:49 2004
> --- postgresql-8.0.0rc2/src/backend/executor/execMain.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 558,563 ****
> --- 558,564 ----
>       /*
>        * Have to lock relations selected for update
>        */
> +     estate->es_nowait = parseTree->nowait;
>       estate->es_rowMark = NIL;
>       if (parseTree->rowMarks != NIL)
>       {
> ***************
> *** 1133,1139 ****
>
>                       tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
>                       test = heap_mark4update(erm->relation, &tuple, &buffer,
> !                                             estate->es_snapshot->curcid);
>                       ReleaseBuffer(buffer);
>                       switch (test)
>                       {
> --- 1134,1140 ----
>
>                       tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
>                       test = heap_mark4update(erm->relation, &tuple, &buffer,
> !                             estate->es_snapshot->curcid, estate->es_nowait);
>                       ReleaseBuffer(buffer);
>                       switch (test)
>                       {
> ***************
> *** 2082,2087 ****
> --- 2083,2089 ----
>       epqstate->es_instrument = estate->es_instrument;
>       epqstate->es_select_into = estate->es_select_into;
>       epqstate->es_into_oids = estate->es_into_oids;
> +     epqstate->es_nowait = estate->es_nowait;
>       epqstate->es_topPlan = estate->es_topPlan;
>
>       /*
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/executor/execUtils.c
postgresql-8.0.0rc2/src/backend/executor/execUtils.c
> *** postgresql-8.0.0rc2.orig/src/backend/executor/execUtils.c    Fri Oct  1 01:21:23 2004
> --- postgresql-8.0.0rc2/src/backend/executor/execUtils.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 203,209 ****
>       estate->es_instrument = false;
>       estate->es_select_into = false;
>       estate->es_into_oids = false;
> !
>       estate->es_exprcontexts = NIL;
>
>       estate->es_per_tuple_exprcontext = NULL;
> --- 203,210 ----
>       estate->es_instrument = false;
>       estate->es_select_into = false;
>       estate->es_into_oids = false;
> !     estate->es_nowait = false;
> !
>       estate->es_exprcontexts = NIL;
>
>       estate->es_per_tuple_exprcontext = NULL;
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/nodes/copyfuncs.c postgresql-8.0.0rc2/src/backend/nodes/copyfuncs.c
> *** postgresql-8.0.0rc2.orig/src/backend/nodes/copyfuncs.c    Sun Dec 12 00:26:33 2004
> --- postgresql-8.0.0rc2/src/backend/nodes/copyfuncs.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 1426,1431 ****
> --- 1426,1442 ----
>       return newnode;
>   }
>
> + static ForUpdate *
> + _copyForUpdate(ForUpdate *from)
> + {
> +     ForUpdate *newnode = makeNode(ForUpdate);
> +
> +     COPY_NODE_FIELD(update_list);
> +     COPY_SCALAR_FIELD(nowait);
> +
> +     return newnode;
> + }
> +
>   static RangeSubselect *
>   _copyRangeSubselect(RangeSubselect *from)
>   {
> ***************
> *** 1537,1542 ****
> --- 1548,1554 ----
>       COPY_NODE_FIELD(groupClause);
>       COPY_NODE_FIELD(havingQual);
>       COPY_NODE_FIELD(distinctClause);
> +     COPY_SCALAR_FIELD(nowait);
>       COPY_NODE_FIELD(sortClause);
>       COPY_NODE_FIELD(limitOffset);
>       COPY_NODE_FIELD(limitCount);
> ***************
> *** 1611,1617 ****
>       COPY_NODE_FIELD(sortClause);
>       COPY_NODE_FIELD(limitOffset);
>       COPY_NODE_FIELD(limitCount);
> !     COPY_NODE_FIELD(forUpdate);
>       COPY_SCALAR_FIELD(op);
>       COPY_SCALAR_FIELD(all);
>       COPY_NODE_FIELD(larg);
> --- 1623,1629 ----
>       COPY_NODE_FIELD(sortClause);
>       COPY_NODE_FIELD(limitOffset);
>       COPY_NODE_FIELD(limitCount);
> !     COPY_NODE_FIELD(forupdateClause);
>       COPY_SCALAR_FIELD(op);
>       COPY_SCALAR_FIELD(all);
>       COPY_NODE_FIELD(larg);
> ***************
> *** 3065,3070 ****
> --- 3077,3085 ----
>           case T_SortBy:
>               retval = _copySortBy(from);
>               break;
> +         case T_ForUpdate:
> +             retval = _copyForUpdate(from);
> +             break;
>           case T_RangeSubselect:
>               retval = _copyRangeSubselect(from);
>               break;
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/nodes/equalfuncs.c postgresql-8.0.0rc2/src/backend/nodes/equalfuncs.c
> *** postgresql-8.0.0rc2.orig/src/backend/nodes/equalfuncs.c    Sun Dec 12 00:26:33 2004
> --- postgresql-8.0.0rc2/src/backend/nodes/equalfuncs.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 656,661 ****
> --- 656,662 ----
>       COMPARE_NODE_FIELD(groupClause);
>       COMPARE_NODE_FIELD(havingQual);
>       COMPARE_NODE_FIELD(distinctClause);
> +     COMPARE_SCALAR_FIELD(nowait);
>       COMPARE_NODE_FIELD(sortClause);
>       COMPARE_NODE_FIELD(limitOffset);
>       COMPARE_NODE_FIELD(limitCount);
> ***************
> *** 719,725 ****
>       COMPARE_NODE_FIELD(sortClause);
>       COMPARE_NODE_FIELD(limitOffset);
>       COMPARE_NODE_FIELD(limitCount);
> !     COMPARE_NODE_FIELD(forUpdate);
>       COMPARE_SCALAR_FIELD(op);
>       COMPARE_SCALAR_FIELD(all);
>       COMPARE_NODE_FIELD(larg);
> --- 720,726 ----
>       COMPARE_NODE_FIELD(sortClause);
>       COMPARE_NODE_FIELD(limitOffset);
>       COMPARE_NODE_FIELD(limitCount);
> !     COMPARE_NODE_FIELD(forupdateClause);
>       COMPARE_SCALAR_FIELD(op);
>       COMPARE_SCALAR_FIELD(all);
>       COMPARE_NODE_FIELD(larg);
> ***************
> *** 1577,1582 ****
> --- 1578,1592 ----
>   }
>
>   static bool
> + _equalForUpdate(ForUpdate *a, ForUpdate *b)
> + {
> +     COMPARE_SCALAR_FIELD(nowait);
> +     COMPARE_NODE_FIELD(update_list);
> +
> +     return true;
> + }
> +
> + static bool
>   _equalRangeSubselect(RangeSubselect *a, RangeSubselect *b)
>   {
>       COMPARE_NODE_FIELD(subquery);
> ***************
> *** 2202,2207 ****
> --- 2212,2220 ----
>           case T_SortBy:
>               retval = _equalSortBy(a, b);
>               break;
> +         case T_ForUpdate:
> +             retval = _equalForUpdate(a, b);
> +             break;
>           case T_RangeSubselect:
>               retval = _equalRangeSubselect(a, b);
>               break;
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/nodes/outfuncs.c postgresql-8.0.0rc2/src/backend/nodes/outfuncs.c
> *** postgresql-8.0.0rc2.orig/src/backend/nodes/outfuncs.c    Sun Dec 12 00:26:33 2004
> --- postgresql-8.0.0rc2/src/backend/nodes/outfuncs.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 1202,1208 ****
>       WRITE_NODE_FIELD(sortClause);
>       WRITE_NODE_FIELD(limitOffset);
>       WRITE_NODE_FIELD(limitCount);
> !     WRITE_NODE_FIELD(forUpdate);
>       WRITE_ENUM_FIELD(op, SetOperation);
>       WRITE_BOOL_FIELD(all);
>       WRITE_NODE_FIELD(larg);
> --- 1202,1208 ----
>       WRITE_NODE_FIELD(sortClause);
>       WRITE_NODE_FIELD(limitOffset);
>       WRITE_NODE_FIELD(limitCount);
> !     WRITE_NODE_FIELD(forupdateClause);
>       WRITE_ENUM_FIELD(op, SetOperation);
>       WRITE_BOOL_FIELD(all);
>       WRITE_NODE_FIELD(larg);
> ***************
> *** 1323,1328 ****
> --- 1323,1329 ----
>       WRITE_NODE_FIELD(groupClause);
>       WRITE_NODE_FIELD(havingQual);
>       WRITE_NODE_FIELD(distinctClause);
> +     WRITE_BOOL_FIELD(nowait);
>       WRITE_NODE_FIELD(sortClause);
>       WRITE_NODE_FIELD(limitOffset);
>       WRITE_NODE_FIELD(limitCount);
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/nodes/readfuncs.c postgresql-8.0.0rc2/src/backend/nodes/readfuncs.c
> *** postgresql-8.0.0rc2.orig/src/backend/nodes/readfuncs.c    Sun Dec 12 00:26:34 2004
> --- postgresql-8.0.0rc2/src/backend/nodes/readfuncs.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 149,154 ****
> --- 149,155 ----
>       READ_NODE_FIELD(groupClause);
>       READ_NODE_FIELD(havingQual);
>       READ_NODE_FIELD(distinctClause);
> +     READ_BOOL_FIELD(nowait);
>       READ_NODE_FIELD(sortClause);
>       READ_NODE_FIELD(limitOffset);
>       READ_NODE_FIELD(limitCount);
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/parser/analyze.c postgresql-8.0.0rc2/src/backend/parser/analyze.c
> *** postgresql-8.0.0rc2.orig/src/backend/parser/analyze.c    Wed Nov 17 00:34:26 2004
> --- postgresql-8.0.0rc2/src/backend/parser/analyze.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 135,141 ****
>                          bool isAddConstraint);
>   static void applyColumnNames(List *dst, List *src);
>   static List *getSetColTypes(ParseState *pstate, Node *node);
> ! static void transformForUpdate(Query *qry, List *forUpdate);
>   static void transformConstraintAttrs(List *constraintList);
>   static void transformColumnType(ParseState *pstate, ColumnDef *column);
>   static void release_pstate_resources(ParseState *pstate);
> --- 135,141 ----
>                          bool isAddConstraint);
>   static void applyColumnNames(List *dst, List *src);
>   static List *getSetColTypes(ParseState *pstate, Node *node);
> ! static void transformForUpdate(Query *qry, Node *forupdateClause);
>   static void transformConstraintAttrs(List *constraintList);
>   static void transformColumnType(ParseState *pstate, ColumnDef *column);
>   static void release_pstate_resources(ParseState *pstate);
> ***************
> *** 1804,1810 ****
>       qry->commandType = CMD_SELECT;
>
>       /* make FOR UPDATE clause available to addRangeTableEntry */
> !     pstate->p_forUpdate = stmt->forUpdate;
>
>       /* process the FROM clause */
>       transformFromClause(pstate, stmt->fromClause);
> --- 1804,1810 ----
>       qry->commandType = CMD_SELECT;
>
>       /* make FOR UPDATE clause available to addRangeTableEntry */
> !     pstate->p_forUpdate = stmt->forupdateClause ? ((ForUpdate *)stmt->forupdateClause)->update_list : NIL;
>
>       /* process the FROM clause */
>       transformFromClause(pstate, stmt->fromClause);
> ***************
> *** 1864,1871 ****
>       if (pstate->p_hasAggs || qry->groupClause)
>           parseCheckAggregates(pstate, qry);
>
> !     if (stmt->forUpdate != NIL)
> !         transformForUpdate(qry, stmt->forUpdate);
>
>       return qry;
>   }
> --- 1864,1871 ----
>       if (pstate->p_hasAggs || qry->groupClause)
>           parseCheckAggregates(pstate, qry);
>
> !     if (stmt->forupdateClause)
> !         transformForUpdate(qry, stmt->forupdateClause);
>
>       return qry;
>   }
> ***************
> *** 1893,1899 ****
>       List       *sortClause;
>       Node       *limitOffset;
>       Node       *limitCount;
> !     List       *forUpdate;
>       Node       *node;
>       ListCell   *left_tlist,
>                  *dtlist;
> --- 1893,1899 ----
>       List       *sortClause;
>       Node       *limitOffset;
>       Node       *limitCount;
> !     Node       *forUpdate;
>       Node       *node;
>       ListCell   *left_tlist,
>                  *dtlist;
> ***************
> *** 1931,1942 ****
>       sortClause = stmt->sortClause;
>       limitOffset = stmt->limitOffset;
>       limitCount = stmt->limitCount;
> !     forUpdate = stmt->forUpdate;
>
>       stmt->sortClause = NIL;
>       stmt->limitOffset = NULL;
>       stmt->limitCount = NULL;
> !     stmt->forUpdate = NIL;
>
>       /* We don't support forUpdate with set ops at the moment. */
>       if (forUpdate)
> --- 1931,1942 ----
>       sortClause = stmt->sortClause;
>       limitOffset = stmt->limitOffset;
>       limitCount = stmt->limitCount;
> !     forUpdate = stmt->forupdateClause;
>
>       stmt->sortClause = NIL;
>       stmt->limitOffset = NULL;
>       stmt->limitCount = NULL;
> !     stmt->forupdateClause = NULL;
>
>       /* We don't support forUpdate with set ops at the moment. */
>       if (forUpdate)
> ***************
> *** 2080,2086 ****
>       if (pstate->p_hasAggs || qry->groupClause)
>           parseCheckAggregates(pstate, qry);
>
> !     if (forUpdate != NIL)
>           transformForUpdate(qry, forUpdate);
>
>       return qry;
> --- 2080,2086 ----
>       if (pstate->p_hasAggs || qry->groupClause)
>           parseCheckAggregates(pstate, qry);
>
> !     if (forUpdate)
>           transformForUpdate(qry, forUpdate);
>
>       return qry;
> ***************
> *** 2105,2111 ****
>                   (errcode(ERRCODE_SYNTAX_ERROR),
>                    errmsg("INTO is only allowed on first SELECT of UNION/INTERSECT/EXCEPT")));
>       /* We don't support forUpdate with set ops at the moment. */
> !     if (stmt->forUpdate)
>           ereport(ERROR,
>                   (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
>                    errmsg("SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT")));
> --- 2105,2111 ----
>                   (errcode(ERRCODE_SYNTAX_ERROR),
>                    errmsg("INTO is only allowed on first SELECT of UNION/INTERSECT/EXCEPT")));
>       /* We don't support forUpdate with set ops at the moment. */
> !     if (stmt->forupdateClause)
>           ereport(ERROR,
>                   (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
>                    errmsg("SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT")));
> ***************
> *** 2125,2131 ****
>       {
>           Assert(stmt->larg != NULL && stmt->rarg != NULL);
>           if (stmt->sortClause || stmt->limitOffset || stmt->limitCount ||
> !             stmt->forUpdate)
>               isLeaf = true;
>           else
>               isLeaf = false;
> --- 2125,2131 ----
>       {
>           Assert(stmt->larg != NULL && stmt->rarg != NULL);
>           if (stmt->sortClause || stmt->limitOffset || stmt->limitCount ||
> !             stmt->forupdateClause)
>               isLeaf = true;
>           else
>               isLeaf = false;
> ***************
> *** 2737,2752 ****
>    * in rewriteHandler.c.
>    */
>   static void
> ! transformForUpdate(Query *qry, List *forUpdate)
>   {
>       List       *rowMarks = qry->rowMarks;
>       ListCell   *l;
>       ListCell   *rt;
> !     Index        i;
>
>       CheckSelectForUpdate(qry);
>
> !     if (linitial(forUpdate) == NULL)
>       {
>           /* all regular tables used in query */
>           i = 0;
> --- 2737,2761 ----
>    * in rewriteHandler.c.
>    */
>   static void
> ! transformForUpdate(Query *qry, Node *forupdateClause)
>   {
>       List       *rowMarks = qry->rowMarks;
>       ListCell   *l;
>       ListCell   *rt;
> !     Index       i;
> !     ForUpdate  *fu = (ForUpdate *) forupdateClause;
> !     ForUpdate  empty;
> !     List       *update_list;
>
>       CheckSelectForUpdate(qry);
>
> !     update_list = fu->update_list;
> !     qry->nowait = fu->nowait;
> !
> !     memset(&empty, 0, sizeof(ForUpdate));
> !     empty.nowait = FALSE;
> !
> !     if (linitial(update_list) == NULL)
>       {
>           /* all regular tables used in query */
>           i = 0;
> ***************
> *** 2768,2774 ****
>                        * FOR UPDATE of subquery is propagated to subquery's
>                        * rels
>                        */
> !                     transformForUpdate(rte->subquery, list_make1(NULL));
>                       break;
>                   default:
>                       /* ignore JOIN, SPECIAL, FUNCTION RTEs */
> --- 2777,2785 ----
>                        * FOR UPDATE of subquery is propagated to subquery's
>                        * rels
>                        */
> !                     empty.update_list = list_make1(NULL);
> !                     transformForUpdate(rte->subquery, (Node *) &empty);
> !                     empty.update_list = NIL;
>                       break;
>                   default:
>                       /* ignore JOIN, SPECIAL, FUNCTION RTEs */
> ***************
> *** 2779,2785 ****
>       else
>       {
>           /* just the named tables */
> !         foreach(l, forUpdate)
>           {
>               char       *relname = strVal(lfirst(l));
>
> --- 2790,2796 ----
>       else
>       {
>           /* just the named tables */
> !         foreach(l, update_list)
>           {
>               char       *relname = strVal(lfirst(l));
>
> ***************
> *** 2804,2810 ****
>                                * FOR UPDATE of subquery is propagated to
>                                * subquery's rels
>                                */
> !                             transformForUpdate(rte->subquery, list_make1(NULL));
>                               break;
>                           case RTE_JOIN:
>                               ereport(ERROR,
> --- 2815,2823 ----
>                                * FOR UPDATE of subquery is propagated to
>                                * subquery's rels
>                                */
> !                             empty.update_list = list_make1(NULL);
> !                             transformForUpdate(rte->subquery, (Node *) &empty);
> !                             empty.update_list = NULL;
>                               break;
>                           case RTE_JOIN:
>                               ereport(ERROR,
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/parser/gram.y postgresql-8.0.0rc2/src/backend/parser/gram.y
> *** postgresql-8.0.0rc2.orig/src/backend/parser/gram.y    Mon Nov  8 05:02:20 2004
> --- postgresql-8.0.0rc2/src/backend/parser/gram.y    Mon Dec 27 10:56:52 2004
> ***************
> *** 87,93 ****
>   static List *extractArgTypes(List *parameters);
>   static SelectStmt *findLeftmostSelect(SelectStmt *node);
>   static void insertSelectOptions(SelectStmt *stmt,
> !                                 List *sortClause, List *forUpdate,
>                                   Node *limitOffset, Node *limitCount);
>   static Node *makeSetOp(SetOperation op, bool all, Node *larg, Node *rarg);
>   static Node *doNegate(Node *n);
> --- 87,93 ----
>   static List *extractArgTypes(List *parameters);
>   static SelectStmt *findLeftmostSelect(SelectStmt *node);
>   static void insertSelectOptions(SelectStmt *stmt,
> !                                 List *sortClause, Node *forUpdate,
>                                   Node *limitOffset, Node *limitCount);
>   static Node *makeSetOp(SetOperation op, bool all, Node *larg, Node *rarg);
>   static Node *doNegate(Node *n);
> ***************
> *** 239,245 ****
>   %type <oncommit> OnCommitOption
>   %type <withoids> OptWithOids WithOidsAs
>
> ! %type <list>    for_update_clause opt_for_update_clause update_list
>   %type <boolean>    opt_all
>
>   %type <node>    join_outer join_qual
> --- 239,247 ----
>   %type <oncommit> OnCommitOption
>   %type <withoids> OptWithOids WithOidsAs
>
> ! %type <node>    for_update_clause opt_for_update_clause
> ! %type <list>    update_list
> !
>   %type <boolean>    opt_all
>
>   %type <node>    join_outer join_qual
> ***************
> *** 4801,4807 ****
>               simple_select                        { $$ = $1; }
>               | select_clause sort_clause
>                   {
> !                     insertSelectOptions((SelectStmt *) $1, $2, NIL,
>                                           NULL, NULL);
>                       $$ = $1;
>                   }
> --- 4803,4809 ----
>               simple_select                        { $$ = $1; }
>               | select_clause sort_clause
>                   {
> !                     insertSelectOptions((SelectStmt *) $1, $2, NULL,
>                                           NULL, NULL);
>                       $$ = $1;
>                   }
> ***************
> *** 4862,4867 ****
> --- 4864,4870 ----
>                       n->whereClause = $6;
>                       n->groupClause = $7;
>                       n->havingClause = $8;
> +                     n->forupdateClause = NULL;
>                       $$ = (Node *)n;
>                   }
>               | select_clause UNION opt_all select_clause
> ***************
> *** 5053,5060 ****
>           ;
>
>   for_update_clause:
> !             FOR UPDATE update_list                    { $$ = $3; }
> !             | FOR READ ONLY                            { $$ = NULL; }
>           ;
>
>   opt_for_update_clause:
> --- 5056,5069 ----
>           ;
>
>   for_update_clause:
> !             FOR UPDATE update_list opt_nowait
> !                 {
> !                     ForUpdate *n = makeNode(ForUpdate);
> !                     n->update_list = $3;
> !                     n->nowait = $4;
> !                     $$ = (Node *) n;
> !                 }
> !             | FOR READ ONLY                            { $$ = NULL; }
>           ;
>
>   opt_for_update_clause:
> ***************
> *** 8284,8290 ****
>    */
>   static void
>   insertSelectOptions(SelectStmt *stmt,
> !                     List *sortClause, List *forUpdate,
>                       Node *limitOffset, Node *limitCount)
>   {
>       /*
> --- 8293,8299 ----
>    */
>   static void
>   insertSelectOptions(SelectStmt *stmt,
> !                     List *sortClause, Node *forUpdate,
>                       Node *limitOffset, Node *limitCount)
>   {
>       /*
> ***************
> *** 8301,8311 ****
>       }
>       if (forUpdate)
>       {
> !         if (stmt->forUpdate)
>               ereport(ERROR,
>                       (errcode(ERRCODE_SYNTAX_ERROR),
>                        errmsg("multiple FOR UPDATE clauses not allowed")));
> !         stmt->forUpdate = forUpdate;
>       }
>       if (limitOffset)
>       {
> --- 8310,8320 ----
>       }
>       if (forUpdate)
>       {
> !         if (stmt->forupdateClause)
>               ereport(ERROR,
>                       (errcode(ERRCODE_SYNTAX_ERROR),
>                        errmsg("multiple FOR UPDATE clauses not allowed")));
> !         stmt->forupdateClause = forUpdate;
>       }
>       if (limitOffset)
>       {
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/parser/parse_type.c
postgresql-8.0.0rc2/src/backend/parser/parse_type.c
> *** postgresql-8.0.0rc2.orig/src/backend/parser/parse_type.c    Wed Dec 15 21:15:17 2004
> --- postgresql-8.0.0rc2/src/backend/parser/parse_type.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 432,438 ****
>           stmt->sortClause != NIL ||
>           stmt->limitOffset != NULL ||
>           stmt->limitCount != NULL ||
> !         stmt->forUpdate != NIL ||
>           stmt->op != SETOP_NONE)
>           goto fail;
>       if (list_length(stmt->targetList) != 1)
> --- 432,438 ----
>           stmt->sortClause != NIL ||
>           stmt->limitOffset != NULL ||
>           stmt->limitCount != NULL ||
> !         stmt->forupdateClause != NULL ||
>           stmt->op != SETOP_NONE)
>           goto fail;
>       if (list_length(stmt->targetList) != 1)
> diff -r -c postgresql-8.0.0rc2.orig/src/backend/storage/lmgr/lmgr.c
postgresql-8.0.0rc2/src/backend/storage/lmgr/lmgr.c
> *** postgresql-8.0.0rc2.orig/src/backend/storage/lmgr/lmgr.c    Thu Sep 16 18:58:33 2004
> --- postgresql-8.0.0rc2/src/backend/storage/lmgr/lmgr.c    Mon Dec 27 10:56:52 2004
> ***************
> *** 393,395 ****
> --- 393,435 ----
>       if (!TransactionIdDidCommit(xid) && !TransactionIdDidAbort(xid))
>           TransactionIdAbort(xid);
>   }
> +
> + /*
> +  * As above, but only lock if we can get the lock without blocking.
> +  * Returns TRUE if the lock was acquired.
> +  */
> + bool
> + ConditionalXactLockTableWait(TransactionId xid)
> + {
> +     LOCKTAG        tag;
> +     TransactionId myxid = GetTopTransactionId();
> +
> +     for (;;)
> +     {
> +         Assert(TransactionIdIsValid(xid));
> +         Assert(!TransactionIdEquals(xid, myxid));
> +
> +         MemSet(&tag, 0, sizeof(tag));
> +         tag.relId = XactLockTableId;
> +         tag.dbId = InvalidOid;
> +         tag.objId.xid = xid;
> +
> +         if (!LockAcquire(LockTableId, &tag, myxid, ShareLock, true))
> +             return FALSE;
> +         LockRelease(LockTableId, &tag, myxid, ShareLock);
> +
> +         if (!TransactionIdIsInProgress(xid))
> +             break;
> +         xid = SubTransGetParent(xid);
> +     }
> +
> +     /*
> +      * Transaction was committed/aborted/crashed - we have to update
> +      * pg_clog if transaction is still marked as running.
> +      */
> +     if (!TransactionIdDidCommit(xid) && !TransactionIdDidAbort(xid))
> +         TransactionIdAbort(xid);
> +
> +     return TRUE;
> + }
> +
> diff -r -c postgresql-8.0.0rc2.orig/src/bin/psql/sql_help.h postgresql-8.0.0rc2/src/bin/psql/sql_help.h
> *** postgresql-8.0.0rc2.orig/src/bin/psql/sql_help.h    Tue Dec 21 05:22:44 2004
> --- postgresql-8.0.0rc2/src/bin/psql/sql_help.h    Mon Dec 27 10:57:05 2004
> ***************
> *** 383,393 ****
>
>       { "SELECT",
>         N_("retrieve rows from a table or view"),
> !       N_("SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]\n    * | expression [ AS output_name ] [, ...]\n
 [ FROM from_item [, ...] ]\n    [ WHERE condition ]\n    [ GROUP BY expression [, ...] ]\n    [ HAVING condition [,
...]]\n    [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]\n    [ ORDER BY expression [ ASC | DESC | USING operator ]
[,...] ]\n    [ LIMIT { count | ALL } ]\n    [ OFFSET start ]\n    [ FOR UPDATE [ OF table_name [, ...] ] ]\n\nwhere
from_itemcan be one of:\n\n    [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]\n    ( select )
[AS ] alias [ ( column_alias [, ...] ) ]\n    function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [,
...]| column_definition [, ...] ) ]\n    function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )\n
from_item[ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]") }, 
>
>       { "SELECT INTO",
>         N_("define a new table from the results of a query"),
> !       N_("SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]\n    * | expression [ AS output_name ] [, ...]\n
 INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table\n    [ FROM from_item [, ...] ]\n    [ WHERE condition ]\n    [ GROUP BY
expression[, ...] ]\n    [ HAVING condition [, ...] ]\n    [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]\n    [
ORDERBY expression [ ASC | DESC | USING operator ] [, ...] ]\n    [ LIMIT { count | ALL } ]\n    [ OFFSET start ]\n
[FOR UPDATE [ OF tablename [, ...] ] ]") }, 
>
>       { "SET",
>         N_("change a run-time parameter"),
> --- 383,393 ----
>
>       { "SELECT",
>         N_("retrieve rows from a table or view"),
> !       N_("SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]\n    * | expression [ AS output_name ] [, ...]\n
 [ FROM from_item [, ...] ]\n    [ WHERE condition ]\n    [ GROUP BY expression [, ...] ]\n    [ HAVING condition [,
...]]\n    [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]\n    [ ORDER BY expression [ ASC | DESC | USING operator ]
[,...] ]\n    [ LIMIT { count | ALL } ]\n    [ OFFSET start ]\n    [ FOR UPDATE [ OF table_name [, ...] ] [NOWAIT]
]\n\nwherefrom_item can be one of:\n\n    [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]\n
(select ) [ AS ] alias [ ( column_alias [, ...] ) ]\n    function_name ( [ argument [, ...] ] ) [ AS ] alias [ (
column_alias[, ...] | column_definition [, ...] ) ]\n    function_name ( [ argument [, ...] ] ) AS ( column_definition
[,...] )\n    from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]") }, 
>
>       { "SELECT INTO",
>         N_("define a new table from the results of a query"),
> !       N_("SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]\n    * | expression [ AS output_name ] [, ...]\n
 INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table\n    [ FROM from_item [, ...] ]\n    [ WHERE condition ]\n    [ GROUP BY
expression[, ...] ]\n    [ HAVING condition [, ...] ]\n    [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]\n    [
ORDERBY expression [ ASC | DESC | USING operator ] [, ...] ]\n    [ LIMIT { count | ALL } ]\n    [ OFFSET start ]\n
[FOR UPDATE [ OF tablename [, ...] ] [NOWAIT] ]") }, 
>
>       { "SET",
>         N_("change a run-time parameter"),
> diff -r -c postgresql-8.0.0rc2.orig/src/include/access/heapam.h postgresql-8.0.0rc2/src/include/access/heapam.h
> *** postgresql-8.0.0rc2.orig/src/include/access/heapam.h    Sun Aug 29 07:06:55 2004
> --- postgresql-8.0.0rc2/src/include/access/heapam.h    Mon Dec 27 10:57:05 2004
> ***************
> *** 164,170 ****
>   extern int heap_update(Relation relation, ItemPointer otid, HeapTuple tup,
>           ItemPointer ctid, CommandId cid, Snapshot crosscheck, bool wait);
>   extern int heap_mark4update(Relation relation, HeapTuple tup,
> !                  Buffer *userbuf, CommandId cid);
>
>   extern Oid    simple_heap_insert(Relation relation, HeapTuple tup);
>   extern void simple_heap_delete(Relation relation, ItemPointer tid);
> --- 164,170 ----
>   extern int heap_update(Relation relation, ItemPointer otid, HeapTuple tup,
>           ItemPointer ctid, CommandId cid, Snapshot crosscheck, bool wait);
>   extern int heap_mark4update(Relation relation, HeapTuple tup,
> !                  Buffer *userbuf, CommandId cid, bool nowait);
>
>   extern Oid    simple_heap_insert(Relation relation, HeapTuple tup);
>   extern void simple_heap_delete(Relation relation, ItemPointer tid);
> diff -r -c postgresql-8.0.0rc2.orig/src/include/nodes/execnodes.h postgresql-8.0.0rc2/src/include/nodes/execnodes.h
> *** postgresql-8.0.0rc2.orig/src/include/nodes/execnodes.h    Sun Dec 12 00:26:49 2004
> --- postgresql-8.0.0rc2/src/include/nodes/execnodes.h    Mon Dec 27 10:56:52 2004
> ***************
> *** 308,313 ****
> --- 308,314 ----
>       bool        es_instrument;    /* true requests runtime instrumentation */
>       bool        es_select_into; /* true if doing SELECT INTO */
>       bool        es_into_oids;    /* true to generate OIDs in SELECT INTO */
> +     bool        es_nowait;    /* SELECT FOR UPDATE NOWAIT */
>
>       List       *es_exprcontexts;    /* List of ExprContexts within EState */
>
> diff -r -c postgresql-8.0.0rc2.orig/src/include/nodes/nodes.h postgresql-8.0.0rc2/src/include/nodes/nodes.h
> *** postgresql-8.0.0rc2.orig/src/include/nodes/nodes.h    Sun Dec 12 00:26:49 2004
> --- postgresql-8.0.0rc2/src/include/nodes/nodes.h    Mon Dec 27 10:56:52 2004
> ***************
> *** 302,307 ****
> --- 302,308 ----
>       T_CompositeTypeStmt,
>       T_InhRelation,
>       T_FunctionParameter,
> +     T_ForUpdate,
>
>       /*
>        * TAGS FOR FUNCTION-CALL CONTEXT AND RESULTINFO NODES (see fmgr.h)
> diff -r -c postgresql-8.0.0rc2.orig/src/include/nodes/parsenodes.h postgresql-8.0.0rc2/src/include/nodes/parsenodes.h
> *** postgresql-8.0.0rc2.orig/src/include/nodes/parsenodes.h    Fri Nov  5 20:16:38 2004
> --- postgresql-8.0.0rc2/src/include/nodes/parsenodes.h    Mon Dec 27 10:56:52 2004
> ***************
> *** 103,108 ****
> --- 103,110 ----
>
>       List       *sortClause;        /* a list of SortClause's */
>
> +     bool       nowait;        /* are we in NOWAIT mode? */
> +
>       Node       *limitOffset;    /* # of result tuples to skip */
>       Node       *limitCount;        /* # of result tuples to return */
>
> ***************
> *** 422,427 ****
> --- 424,439 ----
>       Node       *arg;            /* a (Value *) or a (TypeName *) */
>   } DefElem;
>
> + /*
> +  * ForUpdate -
> +  *       used in raw parsetrees output only
> +  */
> + typedef struct ForUpdate
> + {
> +     NodeTag        type;
> +     List        *update_list;    /* list of tables */
> +     bool        nowait;        /* NOWAIT option */
> + } ForUpdate;
>
>   /****************************************************************************
>    *    Nodes for a Query tree
> ***************
> *** 686,692 ****
>       List       *sortClause;        /* sort clause (a list of SortBy's) */
>       Node       *limitOffset;    /* # of result tuples to skip */
>       Node       *limitCount;        /* # of result tuples to return */
> !     List       *forUpdate;        /* FOR UPDATE clause */
>
>       /*
>        * These fields are used only in upper-level SelectStmts.
> --- 698,704 ----
>       List       *sortClause;        /* sort clause (a list of SortBy's) */
>       Node       *limitOffset;    /* # of result tuples to skip */
>       Node       *limitCount;        /* # of result tuples to return */
> !     Node       *forupdateClause;    /* FOR UPDATE clause (ForUpdate node) */
>
>       /*
>        * These fields are used only in upper-level SelectStmts.
> diff -r -c postgresql-8.0.0rc2.orig/src/include/storage/lmgr.h postgresql-8.0.0rc2/src/include/storage/lmgr.h
> *** postgresql-8.0.0rc2.orig/src/include/storage/lmgr.h    Thu Sep 16 18:58:42 2004
> --- postgresql-8.0.0rc2/src/include/storage/lmgr.h    Mon Dec 27 10:56:52 2004
> ***************
> *** 60,64 ****
> --- 60,65 ----
>   extern void XactLockTableInsert(TransactionId xid);
>   extern void XactLockTableDelete(TransactionId xid);
>   extern void XactLockTableWait(TransactionId xid);
> + extern bool ConditionalXactLockTableWait(TransactionId xid);
>
>   #endif   /* LMGR_H */

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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