diff options
Diffstat (limited to 'src/backend/executor/execAmi.c')
| -rw-r--r-- | src/backend/executor/execAmi.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c index ddcd37ae286..c2cb4b68835 100644 --- a/src/backend/executor/execAmi.c +++ b/src/backend/executor/execAmi.c @@ -6,7 +6,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.83 2005/04/19 22:35:11 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.84 2005/05/15 21:19:54 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -248,6 +248,14 @@ ExecMarkPos(PlanState *node) * ExecRestrPos * * restores the scan position previously saved with ExecMarkPos() + * + * NOTE: the semantics of this are that the first ExecProcNode following + * the restore operation will yield the same tuple as the first one following + * the mark operation. It is unspecified what happens to the plan node's + * result TupleTableSlot. (In most cases the result slot is unchanged by + * a restore, but the node may choose to clear it or to load it with the + * restored-to tuple.) Hence the caller should discard any previously + * returned TupleTableSlot after doing a restore. */ void ExecRestrPos(PlanState *node) @@ -290,6 +298,11 @@ ExecRestrPos(PlanState *node) * XXX Ideally, all plan node types would support mark/restore, and this * wouldn't be needed. For now, this had better match the routines above. * But note the test is on Plan nodetype, not PlanState nodetype. + * + * (However, since the only present use of mark/restore is in mergejoin, + * there is no need to support mark/restore in any plan type that is not + * capable of generating ordered output. So the seqscan, tidscan, and + * functionscan support is actually useless code at present.) */ bool ExecSupportsMarkRestore(NodeTag plantype) |