Re: [PATCHES] NO WAIT ... - Mailing list pgsql-hackers

> Tatsuo Ishii wrote:
> >>I agree with Tom here.  I have used the Oracle NOWAIT feature in the 
> >>past and think it is a great feature IMHO.  But when you need to use it, 
> >>you want it to apply very specifically to a single statement.  Using a 
> >>sledge hammer when you need a tweezers isn't the right way to go.
> > 
> > 
> > Once I have written patches for 7.3 to implement this feature for LOCK
> > statement. For example:
> > 
> > test=# LOCK TABLE sales NO WAIT;
> > ERROR:  Cannot aquire relation lock
> > 
> > If there's enough interest, I will modify and submit it for 7.5.
> > --
> > Tatsuo Ishii
> > 
> > ---------------------------(end of broadcast)---------------------------
> > TIP 8: explain analyze is your friend
> 
> 
> That would be great.
> Many people are asking for that.
> Maybe I have time to implement that for SELECT FOR UPDATE.

Here it is(against 7.3.3).
--
Tatsuo Ishii
*** ./src/backend/access/heap/heapam.c.orig    2003-07-04 09:12:10.000000000 +0900
--- ./src/backend/access/heap/heapam.c    2003-07-12 13:52:43.000000000 +0900
***************
*** 479,484 ****
--- 479,517 ----     return r; } 
+ Relation
+ conditional_relation_open(Oid relationId, LOCKMODE lockmode, bool no_wait)
+ {
+     Relation    r;
+ 
+     Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
+ 
+     /*
+      * increment access statistics
+      */
+     IncrHeapAccessStat(local_open);
+     IncrHeapAccessStat(global_open);
+ 
+     /* The relcache does all the real work... */
+     r = RelationIdGetRelation(relationId);
+ 
+     if (!RelationIsValid(r))
+         elog(ERROR, "Relation %u does not exist", relationId);
+ 
+     if (lockmode != NoLock)
+     {
+         if (no_wait)
+         {
+             if (!ConditionalLockRelation(r, lockmode))
+                 elog(ERROR, "Cannot aquire relation lock");
+         }
+         else
+             LockRelation(r, lockmode);
+     }
+ 
+     return r;
+ }
+  /* ----------------  *        relation_openrv - open any relation specified by a RangeVar  *
*** ./src/backend/commands/lockcmds.c.orig    2003-07-04 09:21:30.000000000 +0900
--- ./src/backend/commands/lockcmds.c    2003-07-12 13:53:30.000000000 +0900
***************
*** 58,64 ****         if (aclresult != ACLCHECK_OK)             aclcheck_error(aclresult, get_rel_name(reloid)); 
!         rel = relation_open(reloid, lockstmt->mode);          /* Currently, we only allow plain tables to be locked
*/        if (rel->rd_rel->relkind != RELKIND_RELATION)
 
--- 58,64 ----         if (aclresult != ACLCHECK_OK)             aclcheck_error(aclresult, get_rel_name(reloid)); 
!         rel = conditional_relation_open(reloid, lockstmt->mode, lockstmt->no_wait);          /* Currently, we only
allowplain tables to be locked */         if (rel->rd_rel->relkind != RELKIND_RELATION)
 
*** ./src/backend/parser/gram.y.orig    2003-07-12 12:45:30.000000000 +0900
--- ./src/backend/parser/gram.y    2003-07-12 13:37:27.000000000 +0900
***************
*** 161,166 ****
--- 161,167 ----  %type <ival>    opt_lock lock_type cast_context %type <boolean>    opt_force opt_or_replace
+ %type <boolean>    opt_no_wait  %type <list>    user_list 
***************
*** 392,397 ****
--- 393,400 ----     VACUUM VALID VALIDATOR VALUES VARCHAR VARYING     VERBOSE VERSION VIEW VOLATILE 
+     WAIT
+      WHEN WHERE WITH WITHOUT WORK WRITE      YEAR_P
***************
*** 4050,4061 ****                 }         ; 
! LockStmt:    LOCK_P opt_table qualified_name_list opt_lock                 {                     LockStmt *n =
makeNode(LockStmt);                     n->relations = $3;                     n->mode = $4;                     $$ =
(Node*)n;                 }         ;
 
--- 4053,4065 ----                 }         ; 
! LockStmt:    LOCK_P opt_table qualified_name_list opt_lock opt_no_wait                 {                     LockStmt
*n= makeNode(LockStmt);                      n->relations = $3;                     n->mode = $4;
 
+                     n->no_wait = $5;                     $$ = (Node *)n;                 }         ;
***************
*** 4074,4079 ****
--- 4078,4087 ----             | ACCESS EXCLUSIVE                { $$ = AccessExclusiveLock; }         ; 
+ opt_no_wait:    NO WAIT             { $$ = TRUE; }
+             | /*EMPTY*/                        { $$ = FALSE; }
+         ;
+   /*****************************************************************************  *
*** ./src/backend/parser/keywords.c.orig    2003-07-12 13:39:23.000000000 +0900
--- ./src/backend/parser/keywords.c    2003-07-12 13:39:47.000000000 +0900
***************
*** 318,323 ****
--- 318,324 ----     {"version", VERSION},     {"view", VIEW},     {"volatile", VOLATILE},
+     {"wait", WAIT},     {"when", WHEN},     {"where", WHERE},     {"with", WITH},
*** ./src/include/nodes/parsenodes.h.orig    2003-07-12 12:48:48.000000000 +0900
--- ./src/include/nodes/parsenodes.h    2003-07-12 13:44:04.000000000 +0900
***************
*** 1593,1598 ****
--- 1593,1599 ----     NodeTag        type;     List       *relations;        /* relations to lock */     int
mode;            /* lock mode */
 
+     bool        no_wait;        /* no wait mode */ } LockStmt;  /* ----------------------
*** src/include/access/heapam.h.orig    2003-07-19 14:08:22.000000000 +0900
--- src/include/access/heapam.h    2003-07-19 14:08:48.000000000 +0900
***************
*** 136,141 ****
--- 136,142 ---- /* heapam.c */  extern Relation relation_open(Oid relationId, LOCKMODE lockmode);
+ extern Relation conditional_relation_open(Oid relationId, LOCKMODE lockmode, bool no_wait); extern Relation
relation_openrv(constRangeVar *relation, LOCKMODE lockmode); extern Relation relation_openr(const char
*sysRelationName,LOCKMODE lockmode); extern void relation_close(Relation relation, LOCKMODE lockmode);