diff options
Diffstat (limited to 'src/backend/executor/execAmi.c')
| -rw-r--r-- | src/backend/executor/execAmi.c | 49 |
1 files changed, 13 insertions, 36 deletions
diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c index 643aaace3a..7027d7f805 100644 --- a/src/backend/executor/execAmi.c +++ b/src/backend/executor/execAmi.c @@ -271,16 +271,20 @@ ExecReScan(PlanState *node) * ExecMarkPos * * Marks the current scan position. + * + * NOTE: mark/restore capability is currently needed only for plan nodes + * that are the immediate inner child of a MergeJoin node. Since MergeJoin + * requires sorted input, there is never any need to support mark/restore in + * node types that cannot produce sorted output. There are some cases in + * which a node can pass through sorted data from its child; if we don't + * implement mark/restore for such a node type, the planner compensates by + * inserting a Material node above that node. */ void ExecMarkPos(PlanState *node) { switch (nodeTag(node)) { - case T_SeqScanState: - ExecSeqMarkPos((SeqScanState *) node); - break; - case T_IndexScanState: ExecIndexMarkPos((IndexScanState *) node); break; @@ -289,14 +293,6 @@ ExecMarkPos(PlanState *node) ExecIndexOnlyMarkPos((IndexOnlyScanState *) node); break; - case T_TidScanState: - ExecTidMarkPos((TidScanState *) node); - break; - - case T_ValuesScanState: - ExecValuesMarkPos((ValuesScanState *) node); - break; - case T_CustomScanState: ExecCustomMarkPos((CustomScanState *) node); break; @@ -338,10 +334,6 @@ ExecRestrPos(PlanState *node) { switch (nodeTag(node)) { - case T_SeqScanState: - ExecSeqRestrPos((SeqScanState *) node); - break; - case T_IndexScanState: ExecIndexRestrPos((IndexScanState *) node); break; @@ -350,14 +342,6 @@ ExecRestrPos(PlanState *node) ExecIndexOnlyRestrPos((IndexOnlyScanState *) node); break; - case T_TidScanState: - ExecTidRestrPos((TidScanState *) node); - break; - - case T_ValuesScanState: - ExecValuesRestrPos((ValuesScanState *) node); - break; - case T_CustomScanState: ExecCustomRestrPos((CustomScanState *) node); break; @@ -386,14 +370,6 @@ ExecRestrPos(PlanState *node) * This is used during planning and so must accept a Path, not a Plan. * We keep it here to be adjacent to the routines above, which also must * know which plan types support mark/restore. - * - * 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. - * - * (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 valuesscan support is actually useless code at present.) */ bool ExecSupportsMarkRestore(Path *pathnode) @@ -405,11 +381,8 @@ ExecSupportsMarkRestore(Path *pathnode) */ switch (pathnode->pathtype) { - case T_SeqScan: case T_IndexScan: case T_IndexOnlyScan: - case T_TidScan: - case T_ValuesScan: case T_Material: case T_Sort: return true; @@ -426,7 +399,11 @@ ExecSupportsMarkRestore(Path *pathnode) * Although Result supports mark/restore if it has a child plan * that does, we presently come here only for ResultPath nodes, * which represent Result plans without a child plan. So there is - * nothing to recurse to and we can just say "false". + * nothing to recurse to and we can just say "false". (This means + * that Result's support for mark/restore is in fact dead code. + * We keep it since it's not much code, and someday the planner + * might be smart enough to use it. That would require making + * this function smarter too, of course.) */ Assert(IsA(pathnode, ResultPath)); return false; |