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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
Download Patch File Download Diff File Expand all files Collapse all files

53
src/backend/access/common/heaptuple.c
View File

@ -83,6 +83,10 @@
#define VARLENA_ATT_IS_PACKABLE(att) \
((att)->attstorage != TYPSTORAGE_PLAIN)
/* FormData_pg_attribute.attstorage != TYPSTORAGE_PLAIN and an attlen of -1 */
#define COMPACT_ATTR_IS_PACKABLE(att) \
((att)->attlen == -1 && (att)->attispackable)
/*
* Setup for caching pass-by-ref missing attributes in a way that survives
* tupleDesc destruction.
@ -147,12 +151,12 @@ Datum
getmissingattr(TupleDesc tupleDesc,
int attnum, bool *isnull)
{
Form_pg_attribute att;
CompactAttribute *att;
Assert(attnum <= tupleDesc->natts);
Assert(attnum > 0);
att = TupleDescAttr(tupleDesc, attnum - 1);
att = TupleDescCompactAttr(tupleDesc, attnum - 1);
if (att->atthasmissing)
{
@ -223,15 +227,15 @@ heap_compute_data_size(TupleDesc tupleDesc,
for (i = 0; i < numberOfAttributes; i++)
{
Datum val;
Form_pg_attribute atti;
CompactAttribute *atti;
if (isnull[i])
continue;
val = values[i];
atti = TupleDescAttr(tupleDesc, i);
atti = TupleDescCompactAttr(tupleDesc, i);
if (ATT_IS_PACKABLE(atti) &&
if (COMPACT_ATTR_IS_PACKABLE(atti) &&
VARATT_CAN_MAKE_SHORT(DatumGetPointer(val)))
{
/*
@ -268,7 +272,7 @@ heap_compute_data_size(TupleDesc tupleDesc,
* Fill in either a data value or a bit in the null bitmask
*/
static inline void
fill_val(Form_pg_attribute att,
fill_val(CompactAttribute *att,
bits8 **bit,
int *bitmask,
char **dataP,
@ -349,8 +353,7 @@ fill_val(Form_pg_attribute att,
data_length = VARSIZE_SHORT(val);
memcpy(data, val, data_length);
}
else if (VARLENA_ATT_IS_PACKABLE(att) &&
VARATT_CAN_MAKE_SHORT(val))
else if (att->attispackable && VARATT_CAN_MAKE_SHORT(val))
{
/* convert to short varlena -- no alignment */
data_length = VARATT_CONVERTED_SHORT_SIZE(val);
@ -427,7 +430,7 @@ heap_fill_tuple(TupleDesc tupleDesc,
for (i = 0; i < numberOfAttributes; i++)
{
Form_pg_attribute attr = TupleDescAttr(tupleDesc, i);
CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, i);
fill_val(attr,
bitP ? &bitP : NULL,
@ -461,7 +464,8 @@ heap_attisnull(HeapTuple tup, int attnum, TupleDesc tupleDesc)
Assert(!tupleDesc || attnum <= tupleDesc->natts);
if (attnum > (int) HeapTupleHeaderGetNatts(tup->t_data))
{
if (tupleDesc && TupleDescAttr(tupleDesc, attnum - 1)->atthasmissing)
if (tupleDesc &&
TupleDescCompactAttr(tupleDesc, attnum - 1)->atthasmissing)
return false;
else
return true;
@ -570,13 +574,13 @@ nocachegetattr(HeapTuple tup,
if (!slow)
{
Form_pg_attribute att;
CompactAttribute *att;
/*
* If we get here, there are no nulls up to and including the target
* attribute. If we have a cached offset, we can use it.
*/
att = TupleDescAttr(tupleDesc, attnum);
att = TupleDescCompactAttr(tupleDesc, attnum);
if (att->attcacheoff >= 0)
return fetchatt(att, tp + att->attcacheoff);
@ -591,7 +595,7 @@ nocachegetattr(HeapTuple tup,
for (j = 0; j <= attnum; j++)
{
if (TupleDescAttr(tupleDesc, j)->attlen <= 0)
if (TupleDescCompactAttr(tupleDesc, j)->attlen <= 0)
{
slow = true;
break;
@ -614,18 +618,18 @@ nocachegetattr(HeapTuple tup,
* fixed-width columns, in hope of avoiding future visits to this
* routine.
*/
TupleDescAttr(tupleDesc, 0)->attcacheoff = 0;
TupleDescCompactAttr(tupleDesc, 0)->attcacheoff = 0;
/* we might have set some offsets in the slow path previously */
while (j < natts && TupleDescAttr(tupleDesc, j)->attcacheoff > 0)
while (j < natts && TupleDescCompactAttr(tupleDesc, j)->attcacheoff > 0)
j++;
off = TupleDescAttr(tupleDesc, j - 1)->attcacheoff +
TupleDescAttr(tupleDesc, j - 1)->attlen;
off = TupleDescCompactAttr(tupleDesc, j - 1)->attcacheoff +
TupleDescCompactAttr(tupleDesc, j - 1)->attlen;
for (; j < natts; j++)
{
Form_pg_attribute att = TupleDescAttr(tupleDesc, j);
CompactAttribute *att = TupleDescCompactAttr(tupleDesc, j);
if (att->attlen <= 0)
break;
@ -639,7 +643,7 @@ nocachegetattr(HeapTuple tup,
Assert(j > attnum);
off = TupleDescAttr(tupleDesc, attnum)->attcacheoff;
off = TupleDescCompactAttr(tupleDesc, attnum)->attcacheoff;
}
else
{
@ -659,7 +663,7 @@ nocachegetattr(HeapTuple tup,
off = 0;
for (i = 0;; i++) /* loop exit is at "break" */
{
Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
CompactAttribute *att = TupleDescCompactAttr(tupleDesc, i);
if (HeapTupleHasNulls(tup) && att_isnull(i, bp))
{
@ -707,7 +711,7 @@ nocachegetattr(HeapTuple tup,
}
}
return fetchatt(TupleDescAttr(tupleDesc, attnum), tp + off);
return fetchatt(TupleDescCompactAttr(tupleDesc, attnum), tp + off);
}
/* ----------------
@ -892,7 +896,7 @@ expand_tuple(HeapTuple *targetHeapTuple,
{
if (attrmiss[attnum].am_present)
{
Form_pg_attribute att = TupleDescAttr(tupleDesc, attnum);
CompactAttribute *att = TupleDescCompactAttr(tupleDesc, attnum);
targetDataLen = att_align_datum(targetDataLen,
att->attalign,
@ -1020,8 +1024,7 @@ expand_tuple(HeapTuple *targetHeapTuple,
/* Now fill in the missing values */
for (attnum = sourceNatts; attnum < natts; attnum++)
{
Form_pg_attribute attr = TupleDescAttr(tupleDesc, attnum);
CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum);
if (attrmiss && attrmiss[attnum].am_present)
{
@ -1370,7 +1373,7 @@ heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
for (attnum = 0; attnum < natts; attnum++)
{
Form_pg_attribute thisatt = TupleDescAttr(tupleDesc, attnum);
CompactAttribute *thisatt = TupleDescCompactAttr(tupleDesc, attnum);
if (hasnulls && att_isnull(attnum, bp))
{