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Commit827d6f9

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Improve performance of find_all_inheritors()
Previous coding uses three nested loops which obviously were a pain forlarge number of table's children. Patch replaces inner loop witha hashmap.Author: Aleksander AlekseevReviewed-by: mehttps://commitfest.postgresql.org/13/1058/
1 parent5196f13 commit827d6f9

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‎src/backend/catalog/pg_inherits.c‎

Lines changed: 44 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -31,7 +31,16 @@
3131
#include"utils/fmgroids.h"
3232
#include"utils/syscache.h"
3333
#include"utils/tqual.h"
34+
#include"utils/memutils.h"
3435

36+
/*
37+
* Entry of a hash table used in find_all_inheritors. See below.
38+
*/
39+
typedefstructSeenRelsEntry
40+
{
41+
Oidrel_id;/* relation oid */
42+
ListCell*numparents_cell;/* corresponding list cell */
43+
}SeenRelsEntry;
3544

3645
/*
3746
* find_inheritance_children
@@ -157,10 +166,33 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
157166
List*
158167
find_all_inheritors(OidparentrelId,LOCKMODElockmode,List**numparents)
159168
{
169+
/* hash table for O(1) rel_oid -> rel_numparents cell lookup */
170+
HTAB*seen_rels;
171+
HASHCTLctl;
172+
MemoryContextnew_ctx;
160173
List*rels_list,
161174
*rel_numparents;
162175
ListCell*l;
163176

177+
/*
178+
* We need a separate memory context for a hash table. This is because
179+
* hash table is used only in this procedure. To free a memory we need to
180+
* call hash_destroy which is just a wrapper around MemoryContextDelete.
181+
*/
182+
new_ctx=AllocSetContextCreate(CurrentMemoryContext,
183+
"FindAllInheritorsSeenRelsContext",
184+
ALLOCSET_DEFAULT_SIZES);
185+
186+
memset(&ctl,0,sizeof(ctl));
187+
ctl.keysize=sizeof(Oid);
188+
ctl.entrysize=sizeof(SeenRelsEntry);
189+
ctl.hcxt=new_ctx;
190+
191+
seen_rels=hash_create(
192+
"find_all_inheritors temporary table",
193+
32,/* start small and extend */
194+
&ctl,HASH_ELEM |HASH_BLOBS |HASH_CONTEXT);
195+
164196
/*
165197
* We build a list starting with the given rel and adding all direct and
166198
* indirect children. We can use a single list as both the record of
@@ -190,26 +222,21 @@ find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
190222
foreach(lc,currentchildren)
191223
{
192224
Oidchild_oid=lfirst_oid(lc);
193-
boolfound= false;
194-
ListCell*lo;
195-
ListCell*li;
225+
boolfound;
226+
SeenRelsEntry*hash_entry;
196227

197-
/* if the rel is already there, bump number-of-parents counter */
198-
forboth(lo,rels_list,li,rel_numparents)
228+
hash_entry=hash_search(seen_rels,&child_oid,HASH_ENTER,&found);
229+
if (found)
199230
{
200-
if (lfirst_oid(lo)==child_oid)
201-
{
202-
lfirst_int(li)++;
203-
found= true;
204-
break;
205-
}
231+
/* if the rel is already there, bump number-of-parents counter */
232+
lfirst_int(hash_entry->numparents_cell)++;
206233
}
207-
208-
/* if it's not there, add it. expect 1 parent, initially. */
209-
if (!found)
234+
else
210235
{
236+
/* if it's not there, add it. expect 1 parent, initially. */
211237
rels_list=lappend_oid(rels_list,child_oid);
212238
rel_numparents=lappend_int(rel_numparents,1);
239+
hash_entry->numparents_cell=rel_numparents->tail;
213240
}
214241
}
215242
}
@@ -218,6 +245,9 @@ find_all_inheritors(Oid parentrelId, LOCKMODE lockmode, List **numparents)
218245
*numparents=rel_numparents;
219246
else
220247
list_free(rel_numparents);
248+
249+
hash_destroy(seen_rels);
250+
221251
returnrels_list;
222252
}
223253

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