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Introduce CompactAttribute array in TupleDesc

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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
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4
src/backend/executor/execTuples.c
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@@ -1044,7 +1044,7 @@ slot_deform_heap_tuple(TupleTableSlot *slot, HeapTuple tuple, uint32 *offp,
for (; attnum < natts; attnum++)
{
Form_pg_attribute thisatt = TupleDescAttr(tupleDesc, attnum);
CompactAttribute *thisatt = TupleDescCompactAttr(tupleDesc, attnum);
if (hasnulls && att_isnull(attnum, bp))
{
@@ -2237,7 +2237,7 @@ BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
*/
for (i = 0; i < natts; i++)
{
if (!TupleDescAttr(tupdesc, i)->attisdropped)
if (!TupleDescCompactAttr(tupdesc, i)->attisdropped)
{
/* Non-dropped attributes */
dvalues[i] = InputFunctionCall(&attinmeta->attinfuncs[i],