From e3a33a9a9f1a6afb80c9b83c1456c1a36fbcb70b Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 8 Jun 2005 23:02:05 +0000
Subject: [PATCH] Marginal hack to avoid spending a lot of time in
find_join_rel during large planning problems: when the list of join rels gets
too long, make an auxiliary hash table that hashes on the identifying
Bitmapset.
---
src/backend/nodes/bitmapset.c | 27 +++++-
src/backend/optimizer/geqo/geqo_eval.c | 30 +++++--
src/backend/optimizer/geqo/geqo_main.c | 3 +-
src/backend/optimizer/plan/planmain.c | 3 +-
src/backend/optimizer/util/relnode.c | 109 +++++++++++++++++++++++--
src/backend/utils/hash/hashfn.c | 26 +++++-
src/include/nodes/bitmapset.h | 5 +-
src/include/nodes/relation.h | 12 ++-
src/include/utils/hsearch.h | 4 +-
9 files changed, 194 insertions(+), 25 deletions(-)
diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c
index 699f0439ffc..5f4ca9a779b 100644
--- a/src/backend/nodes/bitmapset.c
+++ b/src/backend/nodes/bitmapset.c
@@ -14,7 +14,7 @@
* Copyright (c) 2003-2005, PostgreSQL Global Development Group
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.7 2005/01/01 20:44:15 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.8 2005/06/08 23:02:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -763,3 +763,28 @@ bms_first_member(Bitmapset *a)
}
return -1;
}
+
+/*
+ * bms_hash_value - compute a hash key for a Bitmapset
+ *
+ * Note: we must ensure that any two bitmapsets that are bms_equal() will
+ * hash to the same value; in practice this means that trailing all-zero
+ * words cannot affect the result. Longitudinal XOR provides a reasonable
+ * hash value that has this property.
+ */
+uint32
+bms_hash_value(const Bitmapset *a)
+{
+ bitmapword result = 0;
+ int nwords;
+ int wordnum;
+
+ if (a == NULL)
+ return 0; /* All empty sets hash to 0 */
+ nwords = a->nwords;
+ for (wordnum = 0; wordnum < nwords; wordnum++)
+ {
+ result ^= a->words[wordnum];
+ }
+ return (uint32) result;
+}
diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c
index 3460eb5b8e3..5d31ac738e7 100644
--- a/src/backend/optimizer/geqo/geqo_eval.c
+++ b/src/backend/optimizer/geqo/geqo_eval.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/optimizer/geqo/geqo_eval.c,v 1.74 2005/06/05 22:32:55 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_eval.c,v 1.75 2005/06/08 23:02:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -47,7 +47,8 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
MemoryContext oldcxt;
RelOptInfo *joinrel;
Cost fitness;
- List *savelist;
+ int savelength;
+ struct HTAB *savehash;
/*
* Because gimme_tree considers both left- and right-sided trees,
@@ -83,13 +84,19 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* gimme_tree will add entries to root->join_rel_list, which may or may
* not already contain some entries. The newly added entries will be
* recycled by the MemoryContextDelete below, so we must ensure that
- * the list is restored to its former state before exiting. With the
- * new List implementation, the easiest way is to make a duplicate list
- * that gimme_tree can modify.
+ * the list is restored to its former state before exiting. We can
+ * do this by truncating the list to its original length. NOTE this
+ * assumes that any added entries are appended at the end!
+ *
+ * We also must take care not to mess up the outer join_rel_hash,
+ * if there is one. We can do this by just temporarily setting the
+ * link to NULL. (If we are dealing with enough join rels, which we
+ * very likely are, a new hash table will get built and used locally.)
*/
- savelist = evaldata->root->join_rel_list;
+ savelength = list_length(evaldata->root->join_rel_list);
+ savehash = evaldata->root->join_rel_hash;
- evaldata->root->join_rel_list = list_copy(savelist);
+ evaldata->root->join_rel_hash = NULL;
/* construct the best path for the given combination of relations */
joinrel = gimme_tree(tour, num_gene, evaldata);
@@ -105,8 +112,13 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
else
fitness = DBL_MAX;
- /* restore join_rel_list */
- evaldata->root->join_rel_list = savelist;
+ /*
+ * Restore join_rel_list to its former state, and put back original
+ * hashtable if any.
+ */
+ evaldata->root->join_rel_list = list_truncate(evaldata->root->join_rel_list,
+ savelength);
+ evaldata->root->join_rel_hash = savehash;
/* release all the memory acquired within gimme_tree */
MemoryContextSwitchTo(oldcxt);
diff --git a/src/backend/optimizer/geqo/geqo_main.c b/src/backend/optimizer/geqo/geqo_main.c
index f19f5f7c34d..c027f4370c3 100644
--- a/src/backend/optimizer/geqo/geqo_main.c
+++ b/src/backend/optimizer/geqo/geqo_main.c
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_main.c,v 1.49 2005/06/05 22:32:55 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_main.c,v 1.50 2005/06/08 23:02:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -252,7 +252,6 @@ geqo(PlannerInfo *root, int number_of_rels, List *initial_rels)
*/
best_tour = (Gene *) pool->data[0].string;
- /* root->join_rel_list will be modified during this ! */
best_rel = gimme_tree(best_tour, pool->string_length, &evaldata);
if (best_rel == NULL)
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 1c87b24e4c6..50e1bc5ea8c 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -14,7 +14,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.83 2005/06/06 04:13:35 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.84 2005/06/08 23:02:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -116,6 +116,7 @@ query_planner(PlannerInfo *root, List *tlist, double tuple_fraction,
root->base_rel_array = (RelOptInfo **)
palloc0(root->base_rel_array_size * sizeof(RelOptInfo *));
root->join_rel_list = NIL;
+ root->join_rel_hash = NULL;
root->equi_key_list = NIL;
/*
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 996f7691870..fbaf0de83a8 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/util/relnode.c,v 1.68 2005/06/06 04:13:36 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/util/relnode.c,v 1.69 2005/06/08 23:02:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -21,8 +21,15 @@
#include "optimizer/restrictinfo.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
+#include "utils/hsearch.h"
+typedef struct JoinHashEntry
+{
+ Relids join_relids; /* hash key --- MUST BE FIRST */
+ RelOptInfo *join_rel;
+} JoinHashEntry;
+
static RelOptInfo *make_reloptinfo(PlannerInfo *root, int relid,
RelOptKind reloptkind);
static void build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
@@ -197,6 +204,47 @@ find_base_rel(PlannerInfo *root, int relid)
return NULL; /* keep compiler quiet */
}
+/*
+ * build_join_rel_hash
+ * Construct the auxiliary hash table for join relations.
+ */
+static void
+build_join_rel_hash(PlannerInfo *root)
+{
+ HTAB *hashtab;
+ HASHCTL hash_ctl;
+ ListCell *l;
+
+ /* Create the hash table */
+ MemSet(&hash_ctl, 0, sizeof(hash_ctl));
+ hash_ctl.keysize = sizeof(Relids);
+ hash_ctl.entrysize = sizeof(JoinHashEntry);
+ hash_ctl.hash = bitmap_hash;
+ hash_ctl.match = bitmap_match;
+ hash_ctl.hcxt = CurrentMemoryContext;
+ hashtab = hash_create("JoinRelHashTable",
+ 256L,
+ &hash_ctl,
+ HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
+
+ /* Insert all the already-existing joinrels */
+ foreach(l, root->join_rel_list)
+ {
+ RelOptInfo *rel = (RelOptInfo *) lfirst(l);
+ JoinHashEntry *hentry;
+ bool found;
+
+ hentry = (JoinHashEntry *) hash_search(hashtab,
+ &(rel->relids),
+ HASH_ENTER,
+ &found);
+ Assert(!found);
+ hentry->join_rel = rel;
+ }
+
+ root->join_rel_hash = hashtab;
+}
+
/*
* find_join_rel
* Returns relation entry corresponding to 'relids' (a set of RT indexes),
@@ -205,14 +253,44 @@ find_base_rel(PlannerInfo *root, int relid)
RelOptInfo *
find_join_rel(PlannerInfo *root, Relids relids)
{
- ListCell *l;
+ /*
+ * Switch to using hash lookup when list grows "too long". The threshold
+ * is arbitrary and is known only here.
+ */
+ if (!root->join_rel_hash && list_length(root->join_rel_list) > 32)
+ build_join_rel_hash(root);
- foreach(l, root->join_rel_list)
+ /*
+ * Use either hashtable lookup or linear search, as appropriate.
+ *
+ * Note: the seemingly redundant hashkey variable is used to avoid
+ * taking the address of relids; unless the compiler is exceedingly
+ * smart, doing so would force relids out of a register and thus
+ * probably slow down the list-search case.
+ */
+ if (root->join_rel_hash)
{
- RelOptInfo *rel = (RelOptInfo *) lfirst(l);
+ Relids hashkey = relids;
+ JoinHashEntry *hentry;
+
+ hentry = (JoinHashEntry *) hash_search(root->join_rel_hash,
+ &hashkey,
+ HASH_FIND,
+ NULL);
+ if (hentry)
+ return hentry->join_rel;
+ }
+ else
+ {
+ ListCell *l;
- if (bms_equal(rel->relids, relids))
- return rel;
+ foreach(l, root->join_rel_list)
+ {
+ RelOptInfo *rel = (RelOptInfo *) lfirst(l);
+
+ if (bms_equal(rel->relids, relids))
+ return rel;
+ }
}
return NULL;
@@ -329,9 +407,24 @@ build_join_rel(PlannerInfo *root,
jointype, restrictlist);
/*
- * Add the joinrel to the query's joinrel list.
+ * Add the joinrel to the query's joinrel list, and store it into
+ * the auxiliary hashtable if there is one. NB: GEQO requires us
+ * to append the new joinrel to the end of the list!
*/
- root->join_rel_list = lcons(joinrel, root->join_rel_list);
+ root->join_rel_list = lappend(root->join_rel_list, joinrel);
+
+ if (root->join_rel_hash)
+ {
+ JoinHashEntry *hentry;
+ bool found;
+
+ hentry = (JoinHashEntry *) hash_search(root->join_rel_hash,
+ &(joinrel->relids),
+ HASH_ENTER,
+ &found);
+ Assert(!found);
+ hentry->join_rel = joinrel;
+ }
return joinrel;
}
diff --git a/src/backend/utils/hash/hashfn.c b/src/backend/utils/hash/hashfn.c
index 24255f31e6e..c5968658161 100644
--- a/src/backend/utils/hash/hashfn.c
+++ b/src/backend/utils/hash/hashfn.c
@@ -9,13 +9,14 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/hash/hashfn.c,v 1.23 2005/04/14 20:32:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/hash/hashfn.c,v 1.24 2005/06/08 23:02:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
+#include "nodes/bitmapset.h"
#include "utils/hsearch.h"
@@ -53,3 +54,26 @@ oid_hash(const void *key, Size keysize)
/* We don't actually bother to do anything to the OID value ... */
return (uint32) *((const Oid *) key);
}
+
+/*
+ * bitmap_hash: hash function for keys that are (pointers to) Bitmapsets
+ *
+ * Note: don't forget to specify bitmap_match as the match function!
+ */
+uint32
+bitmap_hash(const void *key, Size keysize)
+{
+ Assert(keysize == sizeof(Bitmapset *));
+ return bms_hash_value(*((const Bitmapset * const *) key));
+}
+
+/*
+ * bitmap_match: match function to use with bitmap_hash
+ */
+int
+bitmap_match(const void *key1, const void *key2, Size keysize)
+{
+ Assert(keysize == sizeof(Bitmapset *));
+ return !bms_equal(*((const Bitmapset * const *) key1),
+ *((const Bitmapset * const *) key2));
+}
diff --git a/src/include/nodes/bitmapset.h b/src/include/nodes/bitmapset.h
index 2ba017fc2ee..b831c4e59a1 100644
--- a/src/include/nodes/bitmapset.h
+++ b/src/include/nodes/bitmapset.h
@@ -13,7 +13,7 @@
*
* Copyright (c) 2003-2005, PostgreSQL Global Development Group
*
- * $PostgreSQL: pgsql/src/include/nodes/bitmapset.h,v 1.6 2005/01/01 20:44:28 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/bitmapset.h,v 1.7 2005/06/08 23:02:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -80,4 +80,7 @@ extern Bitmapset *bms_join(Bitmapset *a, Bitmapset *b);
/* support for iterating through the integer elements of a set: */
extern int bms_first_member(Bitmapset *a);
+/* support for hashtables using Bitmapsets as keys: */
+extern uint32 bms_hash_value(const Bitmapset *a);
+
#endif /* BITMAPSET_H */
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 93dc78aece4..7c702f7105a 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.111 2005/06/06 04:13:36 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.112 2005/06/08 23:02:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -72,7 +72,17 @@ typedef struct PlannerInfo
struct RelOptInfo **base_rel_array; /* All one-relation RelOptInfos */
int base_rel_array_size; /* current allocated array len */
+ /*
+ * join_rel_list is a list of all join-relation RelOptInfos we have
+ * considered in this planning run. For small problems we just scan
+ * the list to do lookups, but when there are many join relations we
+ * build a hash table for faster lookups. The hash table is present
+ * and valid when join_rel_hash is not NULL. Note that we still maintain
+ * the list even when using the hash table for lookups; this simplifies
+ * life for GEQO.
+ */
List *join_rel_list; /* list of join-relation RelOptInfos */
+ struct HTAB *join_rel_hash; /* optional hashtable for join relations */
List *equi_key_list; /* list of lists of equijoined
* PathKeyItems */
diff --git a/src/include/utils/hsearch.h b/src/include/utils/hsearch.h
index bb93dea0775..881327a3e03 100644
--- a/src/include/utils/hsearch.h
+++ b/src/include/utils/hsearch.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.36 2005/05/29 04:23:06 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.37 2005/06/08 23:02:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -184,5 +184,7 @@ extern long hash_select_dirsize(long num_entries);
extern uint32 string_hash(const void *key, Size keysize);
extern uint32 tag_hash(const void *key, Size keysize);
extern uint32 oid_hash(const void *key, Size keysize);
+extern uint32 bitmap_hash(const void *key, Size keysize);
+extern int bitmap_match(const void *key1, const void *key2, Size keysize);
#endif /* HSEARCH_H */
--
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