Thread: [HACKERS] xlogfilename
I study source code about wal, and have a question about xlog file name . what does 000000010000000000000001 mean? Someone says that it means tli logid segno. I don't understand.
I think you may reference to function: pg_xlogfile_name in src/backend/access/transam/xlogfuncs.c, it use XLogFileName defined in src/include/access/xlog_internal.h #define XLogFileName(fname, tli, logSegNo) \ snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, \ (uint32)((logSegNo) / XLogSegmentsPerXLogId), \ (uint32) ((logSegNo) % XLogSegmentsPerXLogId)) hope it's helpful for you --Tony On 20/07/2017 16:42, 王刚 wrote: > I study source code about wal, and have a question about xlog file name . what does 000000010000000000000001 mean? Someonesays that it means tli logid segno. I don't understand.
On Thu, Jul 20, 2017 at 10:58 AM, DEV_OPS <devops@ww-it.cn> wrote: > I think you may reference to function: pg_xlogfile_name in > src/backend/access/transam/xlogfuncs.c, it use XLogFileName defined in > src/include/access/xlog_internal.h > > #define XLogFileName(fname, tli, logSegNo) \ > snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, \ > (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \ > (uint32) ((logSegNo) % XLogSegmentsPerXLogId)) > > > hope it's helpful for you The first 8 characters are the timeline number in hexadecimal format. The next 8 characters indicate a segment number, which gets incremented every 256 segments in hexa format. The last 8 characters indicate the current segment number in hexa format. -- Michael
On Thu, 20 Jul 2017 11:02:25 +0200 Michael Paquier <michael.paquier@gmail.com> wrote: > On Thu, Jul 20, 2017 at 10:58 AM, DEV_OPS <devops@ww-it.cn> wrote: > > I think you may reference to function: pg_xlogfile_name in > > src/backend/access/transam/xlogfuncs.c, it use XLogFileName defined in > > src/include/access/xlog_internal.h > > > > #define XLogFileName(fname, tli, logSegNo) \ > > snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, \ > > (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \ > > (uint32) ((logSegNo) % XLogSegmentsPerXLogId)) > > > > > > hope it's helpful for you > > The first 8 characters are the timeline number in hexadecimal format. > The next 8 characters indicate a segment number, which gets > incremented every 256 segments in hexa format. The last 8 characters > indicate the current segment number in hexa format. As far as I understand, XLOG is a logical big file of 256 * 16 MB, and this is split to multiple physical files of 16MB which are called WAL segments. The second 8 characters indicate the id of the logical xlog file, and the last 8 characters indicate the sequencial number of the segment in this xlog. Regards, > -- > Michael > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers -- Yugo Nagata <nagata@sraoss.co.jp>
On 20 July 2017 at 21:33, Yugo Nagata <nagata@sraoss.co.jp> wrote:
On Thu, 20 Jul 2017 11:02:25 +0200
Michael Paquier <michael.paquier@gmail.com> wrote:
> On Thu, Jul 20, 2017 at 10:58 AM, DEV_OPS <devops@ww-it.cn> wrote:
> > I think you may reference to function: pg_xlogfile_name in
> > src/backend/access/transam/xlogfuncs.c, it use XLogFileName defined in
> > src/include/access/xlog_internal.h
> >
> > #define XLogFileName(fname, tli, logSegNo) \
> > snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, \
> > (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \
> > (uint32) ((logSegNo) % XLogSegmentsPerXLogId))
> >
> >
> > hope it's helpful for you
>
> The first 8 characters are the timeline number in hexadecimal format.
> The next 8 characters indicate a segment number, which gets
> incremented every 256 segments in hexa format. The last 8 characters
> indicate the current segment number in hexa format.
As far as I understand, XLOG is a logical big file of 256 * 16 MB,
and this is split to multiple physical files of 16MB which are called
WAL segments. The second 8 characters indicate the id of the logical
xlog file, and the last 8 characters indicate the sequencial number of
the segment in this xlog.
On Fri, 21 Jul 2017 10:11:05 +0800 Craig Ringer <craig@2ndquadrant.com> wrote: > On 20 July 2017 at 21:33, Yugo Nagata <nagata@sraoss.co.jp> wrote: > > > On Thu, 20 Jul 2017 11:02:25 +0200 > > Michael Paquier <michael.paquier@gmail.com> wrote: > > > > > On Thu, Jul 20, 2017 at 10:58 AM, DEV_OPS <devops@ww-it.cn> wrote: > > > > I think you may reference to function: pg_xlogfile_name in > > > > src/backend/access/transam/xlogfuncs.c, it use XLogFileName defined > > in > > > > src/include/access/xlog_internal.h > > > > > > > > #define XLogFileName(fname, tli, logSegNo) \ > > > > snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, \ > > > > (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \ > > > > (uint32) ((logSegNo) % XLogSegmentsPerXLogId)) > > > > > > > > > > > > hope it's helpful for you > > > > > > The first 8 characters are the timeline number in hexadecimal format. > > > The next 8 characters indicate a segment number, which gets > > > incremented every 256 segments in hexa format. The last 8 characters > > > indicate the current segment number in hexa format. > > > > As far as I understand, XLOG is a logical big file of 256 * 16 MB, > > and this is split to multiple physical files of 16MB which are called > > WAL segments. The second 8 characters indicate the id of the logical > > xlog file, and the last 8 characters indicate the sequencial number of > > the segment in this xlog. > > <http://www.postgresql.org/mailpref/pgsql-hackers> > > > > You missed the timeline ID, which is the first 8 digits. Yes, I missed this. Thanks. > > > -- > Craig Ringer http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services -- Yugo Nagata <nagata@sraoss.co.jp>