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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/commands/tablecmds.c
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@@ -980,6 +980,8 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
cookedDefaults = lappend(cookedDefaults, cooked);
attr->atthasdef = true;
}
populate_compact_attribute(descriptor, attnum - 1);
}
/*
@@ -1396,6 +1398,8 @@ BuildDescForRelation(const List *columns)
att->attstorage = entry->storage;
else if (entry->storage_name)
att->attstorage = GetAttributeStorage(att->atttypid, entry->storage_name);
populate_compact_attribute(desc, attnum - 1);
}
return desc;