Re: WAL Log numbering
От | Bruce Momjian |
---|---|
Тема | Re: WAL Log numbering |
Дата | |
Msg-id | 200109220358.f8M3wv624974@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: WAL Log numbering (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-bugs |
Attached is a patch that changes "sequential" to "ever-increasing". > Justin Clift <justin@postgresql.org> writes: > > I would have though that after 00000000000000FE would be > > 0000000000000100, not 0000000100000000. > > This is the intended behavior, I believe. The low-order half is a > 32-bit byte offset DIV XLogSegSize --- we could compress out the zero > bits, but only at the cost of wiring an assumption about XLogSegSize > into the filename format. The reason that 0/FF is missing from the > sequence is stated in xlog.h: > > /* > * We break each logical log file (xlogid value) into 16Mb segments. > * One possible segment at the end of each log file is wasted, to ensure > * that we don't have problems representing last-byte-position-plus-1. > */ > #define XLogSegSize ((uint32) (16*1024*1024)) > #define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize) > #define XLogFileSize (XLogSegsPerFile * XLogSegSize) > > > Just checked through the Interactive docs (not sure which version of 7.1 > > they are) and says the numbers should be sequential. > > This would seem to be an oversimplification in the docs. > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Don't 'kill -9' the postmaster > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 Index: doc/src/sgml/wal.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v retrieving revision 1.9 diff -c -r1.9 wal.sgml *** doc/src/sgml/wal.sgml 2001/09/09 23:52:12 1.9 --- doc/src/sgml/wal.sgml 2001/09/22 03:58:39 *************** *** 137,143 **** divided into 8 kB pages. The log record headers are described in <filename>access/xlog.h</filename>; record content is dependent on the type of event that is being logged. Segment files are given ! sequential numbers as names, starting at <filename>0000000000000000</filename>. The numbers do not wrap, at present, but it should take a very long time to exhaust the available stock of numbers. --- 137,143 ---- divided into 8 kB pages. The log record headers are described in <filename>access/xlog.h</filename>; record content is dependent on the type of event that is being logged. Segment files are given ! ever-increasing numbers as names, starting at <filename>0000000000000000</filename>. The numbers do not wrap, at present, but it should take a very long time to exhaust the available stock of numbers.
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