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Fix joins with compressed chunks #6541

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Jan 23, 2024
Merged

Fix joins with compressed chunks #6541

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2 changes: 2 additions & 0 deletions .unreleased/fix-segmentby-em
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixes: #6424, #6536 Inefficient join plans on compressed hypertables.
Thanks: @coney21 and @GStechschulte for reporting the problem with inefficient join plans on compressed hypertables.
66 changes: 35 additions & 31 deletions tsl/src/nodes/decompress_chunk/decompress_chunk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1447,7 +1447,6 @@ static bool
add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
CompressionInfo *info, EMCreationContext *context)
{
Relids uncompressed_chunk_relids = info->chunk_rel->relids;
ListCell *lc;

TimescaleDBPrivate *compressed_fdw_private =
Expand All @@ -1462,6 +1461,17 @@ add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
Var *var;
Assert(!bms_overlap(cur_em->em_relids, info->compressed_rel->relids));

/*
* We want to base our equivalence member on the hypertable equivalence
* member, not on the uncompressed chunk one, because the latter is
* marked as child itself. This is mostly relevant for PG16 where we
* have to specify a parent for the newly created equivalence member.
*/
if (cur_em->em_is_child)
{
continue;
}

/* only consider EquivalenceMembers that are Vars, possibly with RelabelType, of the
* uncompressed chunk */
var = (Var *) cur_em->em_expr;
Expand All @@ -1470,14 +1480,24 @@ add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
if (!(var && IsA(var, Var)))
continue;

if ((Index) var->varno != info->chunk_rel->relid)
if ((Index) var->varno != info->ht_rel->relid)
continue;

if (var->varattno <= 0)
{
/*
* We can have equivalence members that refer to special variables,
* but these variables can't be segmentby, so we're not interested
* in them here.
*/
continue;
}

/* given that the em is a var of the uncompressed chunk, the relid of the chunk should
* be set on the em */
Assert(bms_overlap(cur_em->em_relids, uncompressed_chunk_relids));
Assert(bms_is_member(info->ht_rel->relid, cur_em->em_relids));

const char *attname = get_attname(info->chunk_rte->relid, var->varattno, false);
const char *attname = get_attname(info->ht_rte->relid, var->varattno, false);

if (!ts_array_is_member(context->settings->fd.segmentby, attname))
continue;
Expand All @@ -1492,7 +1512,8 @@ add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
* transformation might have substituted a constant, but we
* don't want the child member to be marked as constant.
*/
new_relids = bms_difference(cur_em->em_relids, uncompressed_chunk_relids);
new_relids = bms_copy(cur_em->em_relids);
new_relids = bms_del_member(new_relids, info->ht_rel->relid);
new_relids = bms_add_members(new_relids, info->compressed_rel->relids);

/* copied from add_eq_member */
Expand All @@ -1504,17 +1525,21 @@ add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
em->em_is_const = false;
em->em_is_child = true;
em->em_datatype = cur_em->em_datatype;
#if PG16_GE
em->em_jdomain = cur_em->em_jdomain;
em->em_parent = cur_em;
#endif

#if PG16_LT
/*
* For versions less than PG16, transform and set em_nullable_relids similar to
* em_relids. Note that this code assumes parent and child relids are singletons.
*/
Relids new_nullable_relids = cur_em->em_nullable_relids;
if (bms_overlap(new_nullable_relids, uncompressed_chunk_relids))
if (bms_is_member(info->ht_rel->relid, new_nullable_relids))
{
new_nullable_relids =
bms_difference(new_nullable_relids, uncompressed_chunk_relids);
new_nullable_relids = bms_copy(new_nullable_relids);
new_nullable_relids = bms_del_member(new_nullable_relids, info->ht_rel->relid);
new_nullable_relids =
bms_add_members(new_nullable_relids, info->compressed_rel->relids);
}
Expand Down Expand Up @@ -1544,27 +1569,6 @@ add_segmentby_to_equivalence_class(PlannerInfo *root, EquivalenceClass *cur_ec,
compressed_fdw_private->compressed_ec_em_pairs =
lappend(compressed_fdw_private->compressed_ec_em_pairs, list_make2(cur_ec, em));

#if PG16_GE
/* Record EquivalenceMember for the compressed chunk as derived to prevent
* infinite recursion.
*/

foreach (lc, cur_ec->ec_members)
{
EquivalenceMember *p_em = lfirst_node(EquivalenceMember, lc);
/* Assume non-child member are at the beginning */
if (p_em->em_is_child)
break;

RestrictInfo *d = make_simple_restrictinfo_compat(root, p_em->em_expr);
d->parent_ec = cur_ec;
d->left_em = p_em;
d->right_em = em;
cur_ec->ec_derives = lappend(cur_ec->ec_derives, d);
}

#endif

return true;
}
}
Expand All @@ -1575,10 +1579,10 @@ static void
compressed_rel_setup_equivalence_classes(PlannerInfo *root, CompressionInfo *info)
{
EMCreationContext context = {
.uncompressed_relid = info->chunk_rte->relid,
.uncompressed_relid = info->ht_rte->relid,
.compressed_relid = info->compressed_rte->relid,

.uncompressed_relid_idx = info->chunk_rel->relid,
.uncompressed_relid_idx = info->ht_rel->relid,
.compressed_relid_idx = info->compressed_rel->relid,
.settings = info->settings,
};
Expand Down