database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-01 21:31:19 +03:00
Code Activity

Introduce CompactAttribute array in TupleDesc

Browse Source 
The new compact_attrs array stores a few select fields from
FormData_pg_attribute in a more compact way, using only 16 bytes per
column instead of the 104 bytes that FormData_pg_attribute uses.  Using
CompactAttribute allows performance-critical operations such as tuple
deformation to be performed without looking at the FormData_pg_attribute
element in TupleDesc which means fewer cacheline accesses.  With this
change, NAMEDATALEN could be increased with a much smaller negative impact
on performance.

For some workloads, tuple deformation can be the most CPU intensive part
of processing the query.  Some testing with 16 columns on a table
where the first column is variable length showed around a 10% increase in
transactions per second for an OLAP type query performing aggregation on
the 16th column.  However, in certain cases, the increases were much
higher, up to ~25% on one AMD Zen4 machine.

This also makes pg_attribute.attcacheoff redundant.  A follow-on commit
will remove it, thus shrinking the FormData_pg_attribute struct by 4
bytes.

Author: David Rowley
Discussion: https://postgr.es/m/CAApHDvrBztXP3yx=NKNmo3xwFAFhEdyPnvrDg3=M0RhDs+4vYw@mail.gmail.com
Reviewed-by: Andres Freund, Victor Yegorov
This commit is contained in:
David Rowley
2024-12-03 16:50:59 +13:00
parent e4c8865196
commit d28dff3f6c
14 changed files with 246 additions and 68 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
src/include/access/itup.h
View File

@@ -124,11 +124,13 @@ index_getattr(IndexTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
if (!IndexTupleHasNulls(tup))
{
if (TupleDescAttr(tupleDesc, attnum - 1)->attcacheoff >= 0)
CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum - 1);
if (attr->attcacheoff >= 0)
{
return fetchatt(TupleDescAttr(tupleDesc, attnum - 1),
(char *) tup + IndexInfoFindDataOffset(tup->t_info)
+ TupleDescAttr(tupleDesc, attnum - 1)->attcacheoff);
return fetchatt(attr,
(char *) tup + IndexInfoFindDataOffset(tup->t_info) +
attr->attcacheoff);
}
else
return nocache_index_getattr(tup, attnum, tupleDesc);