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Improve commentary about run-time partition pruning data structures.

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No code changes except for a couple of new Asserts.

David Rowley and Tom Lane

Discussion: https://postgr.es/m/CAKJS1f-6GODRNgEtdPxCnAPme2h2hTztB6LmtfdmcYAAOE0kQg@mail.gmail.com
This commit is contained in:
Tom Lane
2018-06-11 17:14:46 -04:00
parent e5d11b91e4
commit 4e23236403
5 changed files with 71 additions and 45 deletions
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39
src/backend/partitioning/partprune.c
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@@ -202,12 +202,17 @@ make_partition_pruneinfo(PlannerInfo *root, List *partition_rels,
int i;
/*
* Allocate two arrays to store the 1-based indexes of the 'subpaths' and
* 'partitioned_rels' by relid.
* Construct two temporary arrays to map from planner relids to subplan
* and sub-partition indexes. For convenience, we use 1-based indexes
* here, so that zero can represent an un-filled array entry.
*/
relid_subplan_map = palloc0(sizeof(int) * root->simple_rel_array_size);
relid_subpart_map = palloc0(sizeof(int) * root->simple_rel_array_size);
/*
* relid_subplan_map maps relid of a leaf partition to the index in
* 'subpaths' of the scan plan for that partition.
*/
i = 1;
foreach(lc, subpaths)
{
@@ -216,17 +221,27 @@ make_partition_pruneinfo(PlannerInfo *root, List *partition_rels,
Assert(IS_SIMPLE_REL(pathrel));
Assert(pathrel->relid < root->simple_rel_array_size);
/* No duplicates please */
Assert(relid_subplan_map[pathrel->relid] == 0);
relid_subplan_map[pathrel->relid] = i++;
}
/* Likewise for the partition_rels */
/*
* relid_subpart_map maps relid of a non-leaf partition to the index in
* 'partition_rels' of that rel (which will also be the index in the
* returned PartitionPruneInfo list of the info for that partition).
*/
i = 1;
foreach(lc, partition_rels)
{
Index rti = lfirst_int(lc);
Assert(rti < root->simple_rel_array_size);
/* No duplicates please */
Assert(relid_subpart_map[rti] == 0);
/* Same rel cannot be both leaf and non-leaf */
Assert(relid_subplan_map[rti] == 0);
relid_subpart_map[rti] = i++;
}
@@ -287,16 +302,16 @@ make_partition_pruneinfo(PlannerInfo *root, List *partition_rels,
return NIL;
}
/*
* Construct the subplan and subpart maps for this partitioning level.
* Here we convert to zero-based indexes, with -1 for empty entries.
* Also construct a Bitmapset of all partitions that are present (that
* is, not pruned already).
*/
subplan_map = (int *) palloc(nparts * sizeof(int));
subpart_map = (int *) palloc(nparts * sizeof(int));
present_parts = NULL;
/*
* Loop over each partition of the partitioned rel and record the
* subpath index for each. Any partitions which are not present in
* the subpaths List will be set to -1, and any sub-partitioned table
* which is not present will also be set to -1.
*/
for (i = 0; i < nparts; i++)
{
RelOptInfo *partrel = subpart->part_rels[i];
@@ -305,12 +320,6 @@ make_partition_pruneinfo(PlannerInfo *root, List *partition_rels,
subplan_map[i] = subplanidx;
subpart_map[i] = subpartidx;
/*
* Record the indexes of all the partition indexes that we have
* subplans or subparts for. This allows an optimization to skip
* attempting any run-time pruning when it's irrelevant.
*/
if (subplanidx >= 0 || subpartidx >= 0)
present_parts = bms_add_member(present_parts, i);
}