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Commit4d0e994

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Add support for partial TOAST decompression
When asked for a slice of a TOAST entry, decompress enough to return theslice instead of decompressing the entire object.For use cases where the slice is at, or near, the beginning of the entry,this avoids a lot of unnecessary decompression work.This changes the signature of pglz_decompress() by adding a boolean toindicate if it's ok for the call to finish before consuming all of thesource or destination buffers.Author: Paul RamseyReviewed-By: Rafia Sabih, Darafei Praliaskouski, Regina ObeDiscussion:https://postgr.es/m/CACowWR07EDm7Y4m2kbhN_jnys%3DBBf9A6768RyQdKm_%3DNpkcaWg%40mail.gmail.com
1 parentd50d172 commit4d0e994

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5 files changed

+70
-36
lines changed

5 files changed

+70
-36
lines changed

‎src/backend/access/heap/tuptoaster.c‎

Lines changed: 36 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -75,6 +75,7 @@ static struct varlena *toast_fetch_datum(struct varlena *attr);
7575
staticstructvarlena*toast_fetch_datum_slice(structvarlena*attr,
7676
int32sliceoffset,int32length);
7777
staticstructvarlena*toast_decompress_datum(structvarlena*attr);
78+
staticstructvarlena*toast_decompress_datum_slice(structvarlena*attr,int32slicelength);
7879
staticinttoast_open_indexes(Relationtoastrel,
7980
LOCKMODElock,
8081
Relation**toastidxs,
@@ -301,7 +302,11 @@ heap_tuple_untoast_attr_slice(struct varlena *attr,
301302
{
302303
structvarlena*tmp=preslice;
303304

304-
preslice=toast_decompress_datum(tmp);
305+
/* Decompress enough to encompass the slice and the offset */
306+
if (slicelength>0&&sliceoffset >=0)
307+
preslice=toast_decompress_datum_slice(tmp,slicelength+sliceoffset);
308+
else
309+
preslice=toast_decompress_datum(tmp);
305310

306311
if (tmp!=attr)
307312
pfree(tmp);
@@ -2272,9 +2277,38 @@ toast_decompress_datum(struct varlena *attr)
22722277
if (pglz_decompress(TOAST_COMPRESS_RAWDATA(attr),
22732278
VARSIZE(attr)-TOAST_COMPRESS_HDRSZ,
22742279
VARDATA(result),
2275-
TOAST_COMPRESS_RAWSIZE(attr))<0)
2280+
TOAST_COMPRESS_RAWSIZE(attr), true)<0)
2281+
elog(ERROR,"compressed data is corrupted");
2282+
2283+
returnresult;
2284+
}
2285+
2286+
2287+
/* ----------
2288+
* toast_decompress_datum_slice -
2289+
*
2290+
* Decompress the front of a compressed version of a varlena datum.
2291+
* offset handling happens in heap_tuple_untoast_attr_slice.
2292+
* Here we just decompress a slice from the front.
2293+
*/
2294+
staticstructvarlena*
2295+
toast_decompress_datum_slice(structvarlena*attr,int32slicelength)
2296+
{
2297+
structvarlena*result;
2298+
int32rawsize;
2299+
2300+
Assert(VARATT_IS_COMPRESSED(attr));
2301+
2302+
result= (structvarlena*)palloc(slicelength+VARHDRSZ);
2303+
2304+
rawsize=pglz_decompress(TOAST_COMPRESS_RAWDATA(attr),
2305+
VARSIZE(attr)-TOAST_COMPRESS_HDRSZ,
2306+
VARDATA(result),
2307+
slicelength, false);
2308+
if (rawsize<0)
22762309
elog(ERROR,"compressed data is corrupted");
22772310

2311+
SET_VARSIZE(result,rawsize+VARHDRSZ);
22782312
returnresult;
22792313
}
22802314

‎src/backend/access/transam/xlogreader.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1425,7 +1425,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
14251425
{
14261426
/* If a backup block image is compressed, decompress it */
14271427
if (pglz_decompress(ptr,bkpb->bimg_len,tmp.data,
1428-
BLCKSZ-bkpb->hole_length)<0)
1428+
BLCKSZ-bkpb->hole_length, true)<0)
14291429
{
14301430
report_invalid_record(record,"invalid compressed image at %X/%X, block %d",
14311431
(uint32) (record->ReadRecPtr >>32),

‎src/backend/utils/adt/varlena.c‎

Lines changed: 13 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1894,7 +1894,7 @@ text_starts_with(PG_FUNCTION_ARGS)
18941894
result= false;
18951895
else
18961896
{
1897-
text*targ1=DatumGetTextPP(arg1);
1897+
text*targ1=text_substring(arg1,1,len2, false);
18981898
text*targ2=DatumGetTextPP(arg2);
18991899

19001900
result= (memcmp(VARDATA_ANY(targ1),VARDATA_ANY(targ2),
@@ -5346,17 +5346,21 @@ text_concat_ws(PG_FUNCTION_ARGS)
53465346
Datum
53475347
text_left(PG_FUNCTION_ARGS)
53485348
{
5349-
text*str=PG_GETARG_TEXT_PP(0);
5350-
constchar*p=VARDATA_ANY(str);
5351-
intlen=VARSIZE_ANY_EXHDR(str);
5352-
intn=PG_GETARG_INT32(1);
5353-
intrlen;
5349+
intn=PG_GETARG_INT32(1);
53545350

53555351
if (n<0)
5356-
n=pg_mbstrlen_with_len(p,len)+n;
5357-
rlen=pg_mbcharcliplen(p,len,n);
5352+
{
5353+
text*str=PG_GETARG_TEXT_PP(0);
5354+
constchar*p=VARDATA_ANY(str);
5355+
intlen=VARSIZE_ANY_EXHDR(str);
5356+
intrlen;
53585357

5359-
PG_RETURN_TEXT_P(cstring_to_text_with_len(p,rlen));
5358+
n=pg_mbstrlen_with_len(p,len)+n;
5359+
rlen=pg_mbcharcliplen(p,len,n);
5360+
PG_RETURN_TEXT_P(cstring_to_text_with_len(p,rlen));
5361+
}
5362+
else
5363+
PG_RETURN_TEXT_P(text_substring(PG_GETARG_DATUM(0),1,n, false));
53605364
}
53615365

53625366
/*

‎src/common/pg_lzcompress.c‎

Lines changed: 19 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -29,7 +29,7 @@
2929
*
3030
*int32
3131
*pglz_decompress(const char *source, int32 slen, char *dest,
32-
*int32 rawsize)
32+
*int32 rawsize, bool check_complete)
3333
*
3434
*source is the compressed input.
3535
*
@@ -44,6 +44,12 @@
4444
*
4545
*rawsize is the length of the uncompressed data.
4646
*
47+
*check_complete is a flag to let us know if -1 should be
48+
*returned in cases where we don't reach the end of the
49+
*source or dest buffers, or not. This should be false
50+
*if the caller is asking for only a partial result and
51+
*true otherwise.
52+
*
4753
*The return value is the number of bytes written in the
4854
*buffer dest, or -1 if decompression fails.
4955
*
@@ -674,13 +680,14 @@ pglz_compress(const char *source, int32 slen, char *dest,
674680
* pglz_decompress -
675681
*
676682
*Decompresses source into dest. Returns the number of bytes
677-
*decompressed in the destination buffer, or -1 if decompression
678-
*fails.
683+
*decompressed in the destination buffer, and *optionally*
684+
*checks that both the source and dest buffers have been
685+
*fully read and written to, respectively.
679686
* ----------
680687
*/
681688
int32
682689
pglz_decompress(constchar*source,int32slen,char*dest,
683-
int32rawsize)
690+
int32rawsize,boolcheck_complete)
684691
{
685692
constunsignedchar*sp;
686693
constunsignedchar*srcend;
@@ -701,8 +708,9 @@ pglz_decompress(const char *source, int32 slen, char *dest,
701708
unsignedcharctrl=*sp++;
702709
intctrlc;
703710

704-
for (ctrlc=0;ctrlc<8&&sp<srcend;ctrlc++)
711+
for (ctrlc=0;ctrlc<8&&sp<srcend&&dp<destend;ctrlc++)
705712
{
713+
706714
if (ctrl&1)
707715
{
708716
/*
@@ -721,25 +729,13 @@ pglz_decompress(const char *source, int32 slen, char *dest,
721729
if (len==18)
722730
len+=*sp++;
723731

724-
/*
725-
* Check for output buffer overrun, to ensure we don't clobber
726-
* memory in case of corrupt input. Note: we must advance dp
727-
* here to ensure the error is detected below the loop. We
728-
* don't simply put the elog inside the loop since that will
729-
* probably interfere with optimization.
730-
*/
731-
if (dp+len>destend)
732-
{
733-
dp+=len;
734-
break;
735-
}
736-
737732
/*
738733
* Now we copy the bytes specified by the tag from OUTPUT to
739734
* OUTPUT. It is dangerous and platform dependent to use
740735
* memcpy() here, because the copied areas could overlap
741736
* extremely!
742737
*/
738+
len=Min(len,destend-dp);
743739
while (len--)
744740
{
745741
*dp=dp[-off];
@@ -752,9 +748,6 @@ pglz_decompress(const char *source, int32 slen, char *dest,
752748
* An unset control bit means LITERAL BYTE. So we just copy
753749
* one from INPUT to OUTPUT.
754750
*/
755-
if (dp >=destend)/* check for buffer overrun */
756-
break;/* do not clobber memory */
757-
758751
*dp++=*sp++;
759752
}
760753

@@ -767,12 +760,15 @@ pglz_decompress(const char *source, int32 slen, char *dest,
767760

768761
/*
769762
* Check we decompressed the right amount.
763+
* If we are slicing, then we won't necessarily
764+
* be at the end of the source or dest buffers
765+
* when we hit a stop, so we don't test them.
770766
*/
771-
if (dp!=destend||sp!=srcend)
767+
if (check_complete&& (dp!=destend||sp!=srcend))
772768
return-1;
773769

774770
/*
775771
* That's it.
776772
*/
777-
returnrawsize;
773+
return(char*)dp-dest;
778774
}

‎src/include/common/pg_lzcompress.h‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -86,6 +86,6 @@ extern const PGLZ_Strategy *const PGLZ_strategy_always;
8686
externint32pglz_compress(constchar*source,int32slen,char*dest,
8787
constPGLZ_Strategy*strategy);
8888
externint32pglz_decompress(constchar*source,int32slen,char*dest,
89-
int32rawsize);
89+
int32rawsize,boolcheck_complete);
9090

9191
#endif/* _PG_LZCOMPRESS_H_ */

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