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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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13
src/backend/utils/cache/typcache.c vendored
View File

@@ -241,12 +241,18 @@ shared_record_table_compare(const void *a, const void *b, size_t size,
TupleDesc t2;
if (k1->shared)
{
t1 = (TupleDesc) dsa_get_address(area, k1->u.shared_tupdesc);
t1->attrs = TupleDescAttrAddress(t1);
}
else
t1 = k1->u.local_tupdesc;
if (k2->shared)
{
t2 = (TupleDesc) dsa_get_address(area, k2->u.shared_tupdesc);
t2->attrs = TupleDescAttrAddress(t2);
}
else
t2 = k2->u.local_tupdesc;
@@ -264,7 +270,10 @@ shared_record_table_hash(const void *a, size_t size, void *arg)
TupleDesc t;
if (k->shared)
{
t = (TupleDesc) dsa_get_address(area, k->u.shared_tupdesc);
t->attrs = TupleDescAttrAddress(t);
}
else
t = k->u.local_tupdesc;
@@ -1867,6 +1876,7 @@ lookup_rowtype_tupdesc_internal(Oid type_id, int32 typmod, bool noError)
tupdesc = (TupleDesc)
dsa_get_address(CurrentSession->area,
entry->shared_tupdesc);
tupdesc->attrs = TupleDescAttrAddress(tupdesc);
Assert(typmod == tupdesc->tdtypmod);
/* We may need to extend the local RecordCacheArray. */
@@ -2953,6 +2963,7 @@ find_or_make_matching_shared_tupledesc(TupleDesc tupdesc)
result = (TupleDesc)
dsa_get_address(CurrentSession->area,
record_table_entry->key.u.shared_tupdesc);
result->attrs = TupleDescAttrAddress(result);
Assert(result->tdrefcount == -1);
return result;
@@ -3016,6 +3027,7 @@ find_or_make_matching_shared_tupledesc(TupleDesc tupdesc)
result = (TupleDesc)
dsa_get_address(CurrentSession->area,
record_table_entry->key.u.shared_tupdesc);
result->attrs = TupleDescAttrAddress(result);
Assert(result->tdrefcount == -1);
return result;
@@ -3028,6 +3040,7 @@ find_or_make_matching_shared_tupledesc(TupleDesc tupdesc)
record_table_entry);
result = (TupleDesc)
dsa_get_address(CurrentSession->area, shared_dp);
result->attrs = TupleDescAttrAddress(result);
Assert(result->tdrefcount == -1);
return result;