Tweak writetup_heap/readtup_heap to avoid storing the tuple identity
and transaction visibility fields of tuples being sorted. These are always uninteresting in a tuple being sorted (if the fields were actually selected, they'd have been pulled out into user columns beforehand). This saves about 24 bytes per row being sorted, which is a useful savings for any but the widest of sort rows. Per recent discussion.
This commit is contained in:
Tom Lane
parent
672f0beb01
commit
7f52e0c50e
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@ -91,7 +91,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.65 2006/03/10 23:19:00 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.66 2006/05/23 21:37:59 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -2329,23 +2329,53 @@ copytup_heap(Tuplesortstate *state, SortTuple *stup, void *tup)
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}
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/*
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* We don't bother to write the HeapTupleData part of the tuple.
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* When writing HeapTuples to tape, we strip off all tuple identity and
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* transaction visibility information, because those fields aren't really
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* interesting for in-memory tuples (they may or may not be valid in the
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* incoming tuples, depending on the plan that's feeding the sort). We
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* only need to store t_natts, t_infomask, the nulls bitmap if any, and
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* the user data.
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*
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* You might think that we could omit storing t_natts, but you'd be wrong:
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* the incoming tuple might be a physical disk tuple with fewer columns
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* than the table's current logical tupdesc.
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*/
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typedef struct TapeTupleHeader
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{
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unsigned int tuplen; /* required header of a tape item */
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int16 natts; /* number of attributes */
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uint16 infomask; /* various flag bits */
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/* nulls bitmap follows if HEAP_HASNULL, then actual tuple data */
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} TapeTupleHeader;
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static void
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writetup_heap(Tuplesortstate *state, int tapenum, SortTuple *stup)
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{
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HeapTuple tuple = (HeapTuple) stup->tuple;
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unsigned int tuplen;
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HeapTupleHeader t_data = tuple->t_data;
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TapeTupleHeader tapehdr;
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unsigned int datalen;
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unsigned int nullslen;
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tuplen = tuple->t_len + sizeof(tuplen);
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Assert(tuple->t_len >= t_data->t_hoff);
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datalen = tuple->t_len - t_data->t_hoff;
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if (HeapTupleHasNulls(tuple))
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nullslen = BITMAPLEN(t_data->t_natts);
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else
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nullslen = 0;
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tapehdr.tuplen = sizeof(TapeTupleHeader) + nullslen + datalen;
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tapehdr.natts = t_data->t_natts;
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tapehdr.infomask = t_data->t_infomask;
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LogicalTapeWrite(state->tapeset, tapenum,
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(void *) &tuplen, sizeof(tuplen));
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(void *) &tapehdr, sizeof(tapehdr));
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if (nullslen)
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LogicalTapeWrite(state->tapeset, tapenum,
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(void *) t_data->t_bits, nullslen);
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LogicalTapeWrite(state->tapeset, tapenum,
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(void *) tuple->t_data, tuple->t_len);
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(char *) t_data + t_data->t_hoff, datalen);
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if (state->randomAccess) /* need trailing length word? */
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LogicalTapeWrite(state->tapeset, tapenum,
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(void *) &tuplen, sizeof(tuplen));
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(void *) &tapehdr.tuplen, sizeof(tapehdr.tuplen));
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FREEMEM(state, GetMemoryChunkSpace(tuple));
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heap_freetuple(tuple);
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@ -2355,22 +2385,59 @@ static void
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readtup_heap(Tuplesortstate *state, SortTuple *stup,
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int tapenum, unsigned int len)
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{
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unsigned int tuplen = len - sizeof(unsigned int) + HEAPTUPLESIZE;
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HeapTuple tuple = (HeapTuple) palloc(tuplen);
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TapeTupleHeader tapehdr;
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unsigned int datalen;
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unsigned int nullslen;
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unsigned int hoff;
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HeapTuple tuple;
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HeapTupleHeader t_data;
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/* read in the rest of the header */
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if (LogicalTapeRead(state->tapeset, tapenum,
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(char *) &tapehdr + sizeof(unsigned int),
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sizeof(tapehdr) - sizeof(unsigned int)) !=
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sizeof(tapehdr) - sizeof(unsigned int))
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elog(ERROR, "unexpected end of data");
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/* reconstruct lengths of null bitmap and data part */
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if (tapehdr.infomask & HEAP_HASNULL)
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nullslen = BITMAPLEN(tapehdr.natts);
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else
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nullslen = 0;
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datalen = len - sizeof(TapeTupleHeader) - nullslen;
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/* determine overhead size of tuple (should match heap_form_tuple) */
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hoff = offsetof(HeapTupleHeaderData, t_bits) + nullslen;
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if (tapehdr.infomask & HEAP_HASOID)
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hoff += sizeof(Oid);
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hoff = MAXALIGN(hoff);
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/* Allocate the space in one chunk, like heap_form_tuple */
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tuple = (HeapTuple) palloc(HEAPTUPLESIZE + hoff + datalen);
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USEMEM(state, GetMemoryChunkSpace(tuple));
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/* reconstruct the HeapTupleData portion */
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tuple->t_len = len - sizeof(unsigned int);
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t_data = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);
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/* make sure unused header fields are zeroed */
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MemSetAligned(t_data, 0, hoff);
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/* reconstruct the HeapTupleData fields */
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tuple->t_len = hoff + datalen;
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ItemPointerSetInvalid(&(tuple->t_self));
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tuple->t_tableOid = InvalidOid;
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tuple->t_data = (HeapTupleHeader) (((char *) tuple) + HEAPTUPLESIZE);
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/* read in the tuple proper */
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if (LogicalTapeRead(state->tapeset, tapenum, (void *) tuple->t_data,
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tuple->t_len) != tuple->t_len)
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tuple->t_data = t_data;
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/* reconstruct the HeapTupleHeaderData fields */
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ItemPointerSetInvalid(&(t_data->t_ctid));
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t_data->t_natts = tapehdr.natts;
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t_data->t_infomask = (tapehdr.infomask & ~HEAP_XACT_MASK)
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| (HEAP_XMIN_INVALID | HEAP_XMAX_INVALID);
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t_data->t_hoff = hoff;
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/* read in the null bitmap if any */
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if (nullslen)
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if (LogicalTapeRead(state->tapeset, tapenum,
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(void *) t_data->t_bits, nullslen) != nullslen)
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elog(ERROR, "unexpected end of data");
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/* and the data proper */
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if (LogicalTapeRead(state->tapeset, tapenum,
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(char *) t_data + hoff, datalen) != datalen)
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elog(ERROR, "unexpected end of data");
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if (state->randomAccess) /* need trailing length word? */
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if (LogicalTapeRead(state->tapeset, tapenum, (void *) &tuplen,
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sizeof(tuplen)) != sizeof(tuplen))
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if (LogicalTapeRead(state->tapeset, tapenum, (void *) &tapehdr.tuplen,
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sizeof(tapehdr.tuplen)) != sizeof(tapehdr.tuplen))
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elog(ERROR, "unexpected end of data");
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stup->tuple = (void *) tuple;
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/* set up first-column key value */
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@ -13,7 +13,7 @@
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* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.19 2006/03/05 15:59:08 momjian Exp $
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* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.20 2006/05/23 21:37:59 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -32,7 +32,11 @@ typedef struct Tuplesortstate Tuplesortstate;
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* We provide two different interfaces to what is essentially the same
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* code: one for sorting HeapTuples and one for sorting IndexTuples.
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* They differ primarily in the way that the sort key information is
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* supplied.
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* supplied. Also, tuplesort.c guarantees to preserve all the header
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* fields of an IndexTuple, but when sorting HeapTuples only the user data
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* is guaranteed preserved, not the "system columns" (tuple identity and
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* transaction visibility info).
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*
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* Yet a third slightly different interface supports sorting bare Datums.
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*/
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