> 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.
You missed the timeline ID, which is the first 8 digits.