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Improve performance of tuple conversion map generation 

Previously convert_tuples_by_name_map naively performed a search of each
outdesc column starting at the first column in indesc and searched each
indesc column until a match was found.  When partitioned tables had many
columns this could result in slow generation of the tuple conversion maps.
For INSERT and UPDATE statements that touched few rows, this could mean a
very large overhead indeed.

We can do a bit better with this loop.  It's quite likely that the columns
in partitioned tables and their partitions are in the same order, so it
makes sense to start searching for each column outer column at the inner
column position 1 after where the previous match was found (per idea from
Alexander Kuzmenkov). This makes the best case search O(N) instead of
O(N^2).  The worst case is still O(N^2), but it seems unlikely that would
happen.

Likewise, in the planner, make_inh_translation_list's search for the
matching column could often end up falling back on an O(N^2) type search.
This commit also improves that by first checking the column that follows
the previous match, instead of the column with the same attnum.  If we
fail to match here we fallback on the syscache's hashtable lookup.

Author: David Rowley
Reviewed-by: Alexander Kuzmenkov
Discussion: https://www.postgresql.org/message-id/CAKJS1f9-wijVgMdRp6_qDMEQDJJ%2BA_n%3DxzZuTmLx5Fz6cwf%2B8A%40mail.gmail.com
This commit is contained in:
Heikki Linnakangas 2018-07-13 19:54:05 +03:00
parent 130beba36d
commit 42f70cd9c3
2 changed files with 48 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
src/backend/access/common/tupconvert.c
View File

@ -295,12 +295,16 @@ convert_tuples_by_name_map(TupleDesc indesc,
const char *msg)
{
AttrNumber *attrMap;
int n;
int outnatts;
int innatts;
int i;
int nextindesc = -1;
n = outdesc->natts;
attrMap = (AttrNumber *) palloc0(n * sizeof(AttrNumber));
for (i = 0; i < n; i++)
outnatts = outdesc->natts;
innatts = indesc->natts;
attrMap = (AttrNumber *) palloc0(outnatts * sizeof(AttrNumber));
for (i = 0; i < outnatts; i++)
{
Form_pg_attribute outatt = TupleDescAttr(outdesc, i);
char *attname;
@ -313,10 +317,27 @@ convert_tuples_by_name_map(TupleDesc indesc,
attname = NameStr(outatt->attname);
atttypid = outatt->atttypid;
atttypmod = outatt->atttypmod;
for (j = 0; j < indesc->natts; j++)
{
Form_pg_attribute inatt = TupleDescAttr(indesc, j);
/*
* Now search for an attribute with the same name in the indesc. It
* seems likely that a partitioned table will have the attributes in
* the same order as the partition, so the search below is optimized
* for that case. It is possible that columns are dropped in one of
* the relations, but not the other, so we use the 'nextindesc'
* counter to track the starting point of the search. If the inner
* loop encounters dropped columns then it will have to skip over
* them, but it should leave 'nextindesc' at the correct position for
* the next outer loop.
*/
for (j = 0; j < innatts; j++)
{
Form_pg_attribute inatt;
nextindesc++;
if (nextindesc >= innatts)
nextindesc = 0;
inatt = TupleDescAttr(indesc, nextindesc);
if (inatt->attisdropped)
continue;
if (strcmp(attname, NameStr(inatt->attname)) == 0)
@ -330,7 +351,7 @@ convert_tuples_by_name_map(TupleDesc indesc,
attname,
format_type_be(outdesc->tdtypeid),
format_type_be(indesc->tdtypeid))));
attrMap[i] = (AttrNumber) (j + 1);
attrMap[i] = inatt->attnum;
break;
}
}
@ -343,7 +364,6 @@ convert_tuples_by_name_map(TupleDesc indesc,
format_type_be(outdesc->tdtypeid),
format_type_be(indesc->tdtypeid))));
}
return attrMap;
}

39
src/backend/optimizer/prep/prepunion.c
View File

@ -51,6 +51,7 @@
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"
typedef struct
@ -1895,9 +1896,11 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
List *vars = NIL;
TupleDesc old_tupdesc = RelationGetDescr(oldrelation);
TupleDesc new_tupdesc = RelationGetDescr(newrelation);
Oid new_relid = RelationGetRelid(newrelation);
int oldnatts = old_tupdesc->natts;
int newnatts = new_tupdesc->natts;
int old_attno;
int new_attno = 0;
for (old_attno = 0; old_attno < oldnatts; old_attno++)
{
@ -1906,7 +1909,6 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
Oid atttypid;
int32 atttypmod;
Oid attcollation;
int new_attno;
att = TupleDescAttr(old_tupdesc, old_attno);
if (att->attisdropped)
@ -1939,29 +1941,25 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
* Otherwise we have to search for the matching column by name.
* There's no guarantee it'll have the same column position, because
* of cases like ALTER TABLE ADD COLUMN and multiple inheritance.
* However, in simple cases it will be the same column number, so try
* that before we go groveling through all the columns.
*
* Note: the test for (att = ...) != NULL cannot fail, it's just a
* notational device to include the assignment into the if-clause.
* However, in simple cases, the relative order of columns is mostly
* the same in both relations, so try the column of newrelation that
* follows immediately after the one that we just found, and if that
* fails, let syscache handle it.
*/
if (old_attno < newnatts &&
(att = TupleDescAttr(new_tupdesc, old_attno)) != NULL &&
!att->attisdropped &&
strcmp(attname, NameStr(att->attname)) == 0)
new_attno = old_attno;
else
if (new_attno >= newnatts ||
(att = TupleDescAttr(new_tupdesc, new_attno))->attisdropped ||
strcmp(attname, NameStr(att->attname)) != 0)
{
for (new_attno = 0; new_attno < newnatts; new_attno++)
{
att = TupleDescAttr(new_tupdesc, new_attno);
if (!att->attisdropped &&
strcmp(attname, NameStr(att->attname)) == 0)
break;
}
if (new_attno >= newnatts)
HeapTuple newtup;
newtup = SearchSysCacheAttName(new_relid, attname);
if (!newtup)
elog(ERROR, "could not find inherited attribute \"%s\" of relation \"%s\"",
attname, RelationGetRelationName(newrelation));
new_attno = ((Form_pg_attribute) GETSTRUCT(newtup))->attnum - 1;
ReleaseSysCache(newtup);
att = TupleDescAttr(new_tupdesc, new_attno);
}
/* Found it, check type and collation match */
@ -1978,6 +1976,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
atttypmod,
attcollation,
0));
new_attno++;
}
*translated_vars = vars;