Re: WAL Log numbering
От | Justin Clift |
---|---|
Тема | Re: WAL Log numbering |
Дата | |
Msg-id | 3BAC7EA9.CA270E0B@postgresql.org обсуждение исходный текст |
Ответ на | Re: WAL Log numbering (Bruce Momjian <pgman@candle.pha.pa.us>) |
Список | pgsql-bugs |
Hi Bruce, Bruce Momjian wrote: > > Attached is a patch that changes "sequential" to "ever-increasing". That's a good idea. :) I was trying to think of the right wording, but I could only think of sentences that were too complex. That one's nice and simple. Regards and best wishes, Justin Clift > > > 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. -- "My grandfather once told me that there are two kinds of people: those who work and those who take the credit. He told me to try to be in the first group; there was less competition there." - Indira Gandhi
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