On 06/25/2018 08:00 AM, David Rowley wrote:
I'd have expected Test 6 to do about 480-500tps. Adding debug to check
why it's not revealed that the search is doing what's expected. I'm
unsure why it has not improved more.
I think I found one possible reason for this slowness. Your patch
behaves as expected when there is a dropped output column, but does one
extra comparison when there is a dropped input column. This backwards
conversion is called from ExecInitRoutingInfo. To fix this, I'd just
keep a persistent inner loop counter (see the attached patch).
Still, fixing this doesn't improve the performance. According to perf
report, updatepd.sql spends 25% of time in strcmp, and updatep.sql about
0.5%, but they are comparing the same column names, even with the same
alignment and relative offsets. I'm completely puzzled by this.
As a side thought, we wouldn't have to go through this if we had a hash
table that is easy to use, or perhaps string interning in catcache.
--
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
diff --git a/src/backend/access/common/tupconvert.c b/src/backend/access/common/tupconvert.c
index 2d0d2f4..573ddd82 100644
--- a/src/backend/access/common/tupconvert.c
+++ b/src/backend/access/common/tupconvert.c
@@ -297,6 +297,7 @@ convert_tuples_by_name_map(TupleDesc indesc,
AttrNumber *attrMap;
int n;
int i;
+ int nextInput = -1;
n = outdesc->natts;
attrMap = (AttrNumber *) palloc0(n * sizeof(AttrNumber));
@@ -315,7 +316,13 @@ convert_tuples_by_name_map(TupleDesc indesc,
atttypmod = outatt->atttypmod;
for (j = 0; j < indesc->natts; j++)
{
- Form_pg_attribute inatt = TupleDescAttr(indesc, j);
+ Form_pg_attribute inatt;
+
+ nextInput++;
+ if (nextInput >= indesc->natts)
+ nextInput = 0;
+
+ inatt = TupleDescAttr(indesc, nextInput);
if (inatt->attisdropped)
continue;
@@ -330,7 +337,7 @@ 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] = (AttrNumber) (nextInput + 1);
break;
}
}
