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robertmhaasrobertmhaas
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tableam: New callback relation_fetch_toast_slice.
Instead of always calling heap_fetch_toast_slice during detoasting, invoke a table AM callback which, when the toast table is a heap table, will be heap_fetch_toast_slice. This makes it possible for a table AM other than heap to be used as a TOAST table. It also completes the series of commits intended to improve the interaction of tableam with TOAST that began with commit 8b94dab; detoast.c is now, hopefully, fully AM-independent. Patch by me, reviewed by Andres Freund and Peter Eisentraut. Discussion: http://postgr.es/m/CA+TgmoZv-=2iWM4jcw5ZhJeL18HF96+W1yJeYrnGMYdkFFnEpQ@mail.gmail.com
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5 files changed

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-193
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5 files changed

+245
-193
lines changed

‎src/backend/access/common/detoast.c

Lines changed: 6 additions & 193 deletions
Original file line numberDiff line numberDiff line change
@@ -14,22 +14,17 @@
1414
#include "postgres.h"
1515

1616
#include "access/detoast.h"
17-
#include "access/genam.h"
18-
#include "access/heaptoast.h"
1917
#include "access/table.h"
18+
#include "access/tableam.h"
2019
#include "access/toast_internals.h"
2120
#include "common/pg_lzcompress.h"
2221
#include "utils/expandeddatum.h"
23-
#include "utils/fmgroids.h"
2422
#include "utils/rel.h"
2523

2624
static struct varlena *toast_fetch_datum(struct varlena *attr);
2725
static struct varlena *toast_fetch_datum_slice(struct varlena *attr,
2826
int32 sliceoffset,
2927
int32 slicelength);
30-
static void heap_fetch_toast_slice(Relation toastrel, Oid valueid,
31-
int32 attrsize, int32 sliceoffset,
32-
int32 slicelength, struct varlena *result);
3328
static struct varlena *toast_decompress_datum(struct varlena *attr);
3429
static struct varlena *toast_decompress_datum_slice(struct varlena *attr, int32 slicelength);
3530

@@ -356,8 +351,8 @@ toast_fetch_datum(struct varlena *attr)
356351
toastrel = table_open(toast_pointer.va_toastrelid, AccessShareLock);
357352

358353
/* Fetch all chunks */
359-
heap_fetch_toast_slice(toastrel, toast_pointer.va_valueid, attrsize, 0,
360-
attrsize, result);
354+
table_relation_fetch_toast_slice(toastrel, toast_pointer.va_valueid,
355+
attrsize, 0, attrsize, result);
361356

362357
/* Close toast table */
363358
table_close(toastrel, AccessShareLock);
@@ -431,198 +426,16 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset,
431426
toastrel = table_open(toast_pointer.va_toastrelid, AccessShareLock);
432427

433428
/* Fetch all chunks */
434-
heap_fetch_toast_slice(toastrel, toast_pointer.va_valueid, attrsize,
435-
sliceoffset, slicelength, result);
429+
table_relation_fetch_toast_slice(toastrel, toast_pointer.va_valueid,
430+
attrsize, sliceoffset, slicelength,
431+
result);
436432

437433
/* Close toast table */
438434
table_close(toastrel, AccessShareLock);
439435

440436
return result;
441437
}
442438

443-
/*
444-
* Fetch a TOAST slice from a heap table.
445-
*
446-
* toastrel is the relation from which chunks are to be fetched.
447-
* valueid identifies the TOAST value from which chunks are being fetched.
448-
* attrsize is the total size of the TOAST value.
449-
* sliceoffset is the byte offset within the TOAST value from which to fetch.
450-
* slicelength is the number of bytes to be fetched from the TOAST value.
451-
* result is the varlena into which the results should be written.
452-
*/
453-
static void
454-
heap_fetch_toast_slice(Relation toastrel, Oid valueid, int32 attrsize,
455-
int32 sliceoffset, int32 slicelength,
456-
struct varlena *result)
457-
{
458-
Relation *toastidxs;
459-
ScanKeyData toastkey[3];
460-
TupleDesc toasttupDesc = toastrel->rd_att;
461-
int nscankeys;
462-
SysScanDesc toastscan;
463-
HeapTuple ttup;
464-
int32 expectedchunk;
465-
int32 totalchunks = ((attrsize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
466-
int startchunk;
467-
int endchunk;
468-
int num_indexes;
469-
int validIndex;
470-
SnapshotData SnapshotToast;
471-
472-
/* Look for the valid index of toast relation */
473-
validIndex = toast_open_indexes(toastrel,
474-
AccessShareLock,
475-
&toastidxs,
476-
&num_indexes);
477-
478-
startchunk = sliceoffset / TOAST_MAX_CHUNK_SIZE;
479-
endchunk = (sliceoffset + slicelength - 1) / TOAST_MAX_CHUNK_SIZE;
480-
Assert(endchunk <= totalchunks);
481-
482-
/*
483-
* Setup a scan key to fetch from the index. This is either two keys or
484-
* three depending on the number of chunks.
485-
*/
486-
ScanKeyInit(&toastkey[0],
487-
(AttrNumber) 1,
488-
BTEqualStrategyNumber, F_OIDEQ,
489-
ObjectIdGetDatum(valueid));
490-
491-
/*
492-
* No additional condition if fetching all chunks. Otherwise, use an
493-
* equality condition for one chunk, and a range condition otherwise.
494-
*/
495-
if (startchunk == 0 && endchunk == totalchunks - 1)
496-
nscankeys = 1;
497-
else if (startchunk == endchunk)
498-
{
499-
ScanKeyInit(&toastkey[1],
500-
(AttrNumber) 2,
501-
BTEqualStrategyNumber, F_INT4EQ,
502-
Int32GetDatum(startchunk));
503-
nscankeys = 2;
504-
}
505-
else
506-
{
507-
ScanKeyInit(&toastkey[1],
508-
(AttrNumber) 2,
509-
BTGreaterEqualStrategyNumber, F_INT4GE,
510-
Int32GetDatum(startchunk));
511-
ScanKeyInit(&toastkey[2],
512-
(AttrNumber) 2,
513-
BTLessEqualStrategyNumber, F_INT4LE,
514-
Int32GetDatum(endchunk));
515-
nscankeys = 3;
516-
}
517-
518-
/* Prepare for scan */
519-
init_toast_snapshot(&SnapshotToast);
520-
toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
521-
&SnapshotToast, nscankeys, toastkey);
522-
523-
/*
524-
* Read the chunks by index
525-
*
526-
* The index is on (valueid, chunkidx) so they will come in order
527-
*/
528-
expectedchunk = startchunk;
529-
while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
530-
{
531-
int32 curchunk;
532-
Pointer chunk;
533-
bool isnull;
534-
char *chunkdata;
535-
int32 chunksize;
536-
int32 expected_size;
537-
int32 chcpystrt;
538-
int32 chcpyend;
539-
540-
/*
541-
* Have a chunk, extract the sequence number and the data
542-
*/
543-
curchunk = DatumGetInt32(fastgetattr(ttup, 2, toasttupDesc, &isnull));
544-
Assert(!isnull);
545-
chunk = DatumGetPointer(fastgetattr(ttup, 3, toasttupDesc, &isnull));
546-
Assert(!isnull);
547-
if (!VARATT_IS_EXTENDED(chunk))
548-
{
549-
chunksize = VARSIZE(chunk) - VARHDRSZ;
550-
chunkdata = VARDATA(chunk);
551-
}
552-
else if (VARATT_IS_SHORT(chunk))
553-
{
554-
/* could happen due to heap_form_tuple doing its thing */
555-
chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
556-
chunkdata = VARDATA_SHORT(chunk);
557-
}
558-
else
559-
{
560-
/* should never happen */
561-
elog(ERROR, "found toasted toast chunk for toast value %u in %s",
562-
valueid, RelationGetRelationName(toastrel));
563-
chunksize = 0; /* keep compiler quiet */
564-
chunkdata = NULL;
565-
}
566-
567-
/*
568-
* Some checks on the data we've found
569-
*/
570-
if (curchunk != expectedchunk)
571-
ereport(ERROR,
572-
(errcode(ERRCODE_DATA_CORRUPTED),
573-
errmsg_internal("unexpected chunk number %d (expected %d) for toast value %u in %s",
574-
curchunk, expectedchunk, valueid,
575-
RelationGetRelationName(toastrel))));
576-
if (curchunk > endchunk)
577-
ereport(ERROR,
578-
(errcode(ERRCODE_DATA_CORRUPTED),
579-
errmsg_internal("unexpected chunk number %d (out of range %d..%d) for toast value %u in %s",
580-
curchunk,
581-
startchunk, endchunk, valueid,
582-
RelationGetRelationName(toastrel))));
583-
expected_size = curchunk < totalchunks - 1 ? TOAST_MAX_CHUNK_SIZE
584-
: attrsize - ((totalchunks - 1) * TOAST_MAX_CHUNK_SIZE);
585-
if (chunksize != expected_size)
586-
ereport(ERROR,
587-
(errcode(ERRCODE_DATA_CORRUPTED),
588-
errmsg_internal("unexpected chunk size %d (expected %d) in chunk %d of %d for toast value %u in %s",
589-
chunksize, expected_size,
590-
curchunk, totalchunks, valueid,
591-
RelationGetRelationName(toastrel))));
592-
593-
/*
594-
* Copy the data into proper place in our result
595-
*/
596-
chcpystrt = 0;
597-
chcpyend = chunksize - 1;
598-
if (curchunk == startchunk)
599-
chcpystrt = sliceoffset % TOAST_MAX_CHUNK_SIZE;
600-
if (curchunk == endchunk)
601-
chcpyend = (sliceoffset + slicelength - 1) % TOAST_MAX_CHUNK_SIZE;
602-
603-
memcpy(VARDATA(result) +
604-
(curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
605-
chunkdata + chcpystrt,
606-
(chcpyend - chcpystrt) + 1);
607-
608-
expectedchunk++;
609-
}
610-
611-
/*
612-
* Final checks that we successfully fetched the datum
613-
*/
614-
if (expectedchunk != (endchunk + 1))
615-
ereport(ERROR,
616-
(errcode(ERRCODE_DATA_CORRUPTED),
617-
errmsg_internal("missing chunk number %d for toast value %u in %s",
618-
expectedchunk, valueid,
619-
RelationGetRelationName(toastrel))));
620-
621-
/* End scan and close indexes. */
622-
systable_endscan_ordered(toastscan);
623-
toast_close_indexes(toastidxs, num_indexes, AccessShareLock);
624-
}
625-
626439
/* ----------
627440
* toast_decompress_datum -
628441
*

‎src/backend/access/heap/heapam_handler.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2545,6 +2545,7 @@ static const TableAmRoutine heapam_methods = {
25452545
.relation_size = table_block_relation_size,
25462546
.relation_needs_toast_table = heapam_relation_needs_toast_table,
25472547
.relation_toast_am = heapam_relation_toast_am,
2548+
.relation_fetch_toast_slice = heap_fetch_toast_slice,
25482549

25492550
.relation_estimate_size = heapam_estimate_rel_size,
25502551

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