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Use pg_pread() and pg_pwrite() for data files and WAL.

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Cut down on system calls by doing random I/O using offset-based OS
routines where available.  Remove the code for tracking the 'virtual'
seek position.  The only reason left to call FileSeek() was to get
the file's size, so provide a new function FileSize() instead.

Author: Oskari Saarenmaa, Thomas Munro
Reviewed-by: Thomas Munro, Jesper Pedersen, Tom Lane, Alvaro Herrera
Discussion: https://postgr.es/m/CAEepm=02rapCpPR3ZGF2vW=SBHSdFYO_bz_f-wwWJonmA3APgw@mail.gmail.com
Discussion: https://postgr.es/m/b8748d39-0b19-0514-a1b9-4e5a28e6a208%40gmail.com
Discussion: https://postgr.es/m/a86bd200-ebbe-d829-e3ca-0c4474b2fcb7%40ohmu.fi
This commit is contained in:
Thomas Munro
2018-11-07 09:51:50 +13:00
parent 3fd2a7932e
commit c24dcd0cfd
6 changed files with 42 additions and 288 deletions
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30
src/backend/access/transam/xlog.c
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@ -2478,18 +2478,6 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
Size nleft;
int written;
/* Need to seek in the file? */
if (openLogOff != startoffset)
{
if (lseek(openLogFile, (off_t) startoffset, SEEK_SET) < 0)
ereport(PANIC,
(errcode_for_file_access(),
errmsg("could not seek in log file %s to offset %u: %m",
XLogFileNameP(ThisTimeLineID, openLogSegNo),
startoffset)));
openLogOff = startoffset;
}
/* OK to write the page(s) */
from = XLogCtl->pages + startidx * (Size) XLOG_BLCKSZ;
nbytes = npages * (Size) XLOG_BLCKSZ;
@ -2498,7 +2486,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
{
errno = 0;
pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
written = write(openLogFile, from, nleft);
written = pg_pwrite(openLogFile, from, nleft, startoffset);
pgstat_report_wait_end();
if (written <= 0)
{
@ -2513,6 +2501,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
}
nleft -= written;
from += written;
startoffset += written;
} while (nleft > 0);
/* Update state for write */
@ -11821,22 +11810,9 @@ retry:
/* Read the requested page */
readOff = targetPageOff;
if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
{
char fname[MAXFNAMELEN];
int save_errno = errno;
XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
errno = save_errno;
ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
(errcode_for_file_access(),
errmsg("could not seek in log segment %s to offset %u: %m",
fname, readOff)));
goto next_record_is_invalid;
}
pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
r = read(readFile, readBuf, XLOG_BLCKSZ);
r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
if (r != XLOG_BLCKSZ)
{
char fname[MAXFNAMELEN];