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Commitce340e5

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Revise pg_pwrite_zeros()
The following changes are made to pg_write_zeros(), the API able towrite series of zeros using vectored I/O:- Add of an "offset" parameter, to write the size from this position(the 'p' of "pwrite" seems to mean position, though POSIX does notoutline ythat directly), hence the name of the routine is incorrect ifit is not able to handle offsets.- Avoid memset() of "zbuffer" on every call.- Avoid initialization of the whole IOV array if not needed.- Group the trailing write() call with the main write() call,simplifying the function logic.Author: Andres FreundReviewed-by: Michael Paquier, Bharath RupireddyDiscussion:https://postgr.es/m/20230215005525.mrrlmqrxzjzhaipl@awork3.anarazel.de
1 parent47c0acc commitce340e5

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4 files changed

+24
-44
lines changed

4 files changed

+24
-44
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2982,7 +2982,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
29822982
* indirect blocks are down on disk. Therefore, fdatasync(2) or
29832983
* O_DSYNC will be sufficient to sync future writes to the log file.
29842984
*/
2985-
rc=pg_pwrite_zeros(fd,wal_segment_size);
2985+
rc=pg_pwrite_zeros(fd,wal_segment_size,0);
29862986

29872987
if (rc<0)
29882988
save_errno=errno;

‎src/bin/pg_basebackup/walmethods.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -222,7 +222,7 @@ dir_open_for_write(WalWriteMethod *wwmethod, const char *pathname,
222222
{
223223
ssize_trc;
224224

225-
rc=pg_pwrite_zeros(fd,pad_to_size);
225+
rc=pg_pwrite_zeros(fd,pad_to_size,0);
226226

227227
if (rc<0)
228228
{

‎src/common/file_utils.c

Lines changed: 21 additions & 41 deletions
Original file line numberDiff line numberDiff line change
@@ -531,68 +531,48 @@ pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
531531
/*
532532
* pg_pwrite_zeros
533533
*
534-
* Writes zeros to file worth "size" bytes, using vectored I/O.
534+
* Writes zeros to file worth "size" bytes at "offset" (from the start of the
535+
* file), using vectored I/O.
535536
*
536537
* Returns the total amount of data written. On failure, a negative value
537538
* is returned with errno set.
538539
*/
539540
ssize_t
540-
pg_pwrite_zeros(intfd,size_tsize)
541+
pg_pwrite_zeros(intfd,size_tsize,off_toffset)
541542
{
542-
PGAlignedBlockzbuffer;/* worth BLCKSZ */
543-
size_tzbuffer_sz;
543+
conststaticPGAlignedBlockzbuffer= {0};/* worth BLCKSZ */
544+
void*zerobuf_addr=unconstify(PGAlignedBlock*,&zbuffer)->data;
544545
structioveciov[PG_IOV_MAX];
545-
intblocks;
546-
size_tremaining_size=0;
547-
inti;
548-
ssize_twritten;
546+
size_tremaining_size=size;
549547
ssize_ttotal_written=0;
550548

551-
zbuffer_sz=sizeof(zbuffer.data);
552-
553-
/* Zero-fill the buffer. */
554-
memset(zbuffer.data,0,zbuffer_sz);
555-
556-
/* Prepare to write out a lot of copies of our zero buffer at once. */
557-
for (i=0;i<lengthof(iov);++i)
558-
{
559-
iov[i].iov_base=zbuffer.data;
560-
iov[i].iov_len=zbuffer_sz;
561-
}
562-
563549
/* Loop, writing as many blocks as we can for each system call. */
564-
blocks=size /zbuffer_sz;
565-
remaining_size=size %zbuffer_sz;
566-
for (i=0;i<blocks;)
550+
while (remaining_size>0)
567551
{
568-
intiovcnt=Min(blocks-i,lengthof(iov));
569-
off_toffset=i*zbuffer_sz;
570-
571-
written=pg_pwritev_with_retry(fd,iov,iovcnt,offset);
552+
intiovcnt=0;
553+
ssize_twritten;
572554

573-
if (written<0)
574-
returnwritten;
575-
576-
i+=iovcnt;
577-
total_written+=written;
578-
}
555+
for (;iovcnt<PG_IOV_MAX&&remaining_size>0;iovcnt++)
556+
{
557+
size_tthis_iov_size;
579558

580-
/* Now, write the remaining size, if any, of the file with zeros. */
581-
if (remaining_size>0)
582-
{
583-
/* We'll never write more than one block here */
584-
intiovcnt=1;
559+
iov[iovcnt].iov_base=zerobuf_addr;
585560

586-
/* Jump on to the end of previously written blocks */
587-
off_toffset=i*zbuffer_sz;
561+
if (remaining_size<BLCKSZ)
562+
this_iov_size=remaining_size;
563+
else
564+
this_iov_size=BLCKSZ;
588565

589-
iov[0].iov_len=remaining_size;
566+
iov[iovcnt].iov_len=this_iov_size;
567+
remaining_size-=this_iov_size;
568+
}
590569

591570
written=pg_pwritev_with_retry(fd,iov,iovcnt,offset);
592571

593572
if (written<0)
594573
returnwritten;
595574

575+
offset+=written;
596576
total_written+=written;
597577
}
598578

‎src/include/common/file_utils.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -44,6 +44,6 @@ extern ssize_t pg_pwritev_with_retry(int fd,
4444
intiovcnt,
4545
off_toffset);
4646

47-
externssize_tpg_pwrite_zeros(intfd,size_tsize);
47+
externssize_tpg_pwrite_zeros(intfd,size_tsize,off_toffset);
4848

4949
#endif/* FILE_UTILS_H */

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