Tom Lane wrote: > Hannu Krosing <[EMAIL PROTECTED]> writes: > > ??hel kenal p??eval, R, 2006-04-14 kell 16:40, kirjutas Tom Lane: > >> If the backup-taker reads, say, 4K at a time then it's > >> certainly possible that it gets a later version of the second half of a > >> page than it got of the first half. I don't know about you, but I sure > >> don't feel comfortable making assumptions at that level about the > >> behavior of tar or cpio. > >> > >> I fear we still have to disable full_page_writes (force it ON) if > >> XLogArchivingActive is on. Comments? > > > Why not just tell the backup-taker to take backups using 8K pages ? > > How? (No, I don't think tar's blocksize options control this > necessarily --- those indicate the blocking factor on the *tape*. > And not everyone uses tar anyway.) > > Even if this would work for all popular backup programs, it seems > far too fragile: the consequence of forgetting the switch would be > silent data corruption, which you might not notice until the slave > had been in live operation for some time.
Yea, it is a problem. Even a 10k read is going to read 2k into the next page. I am thinking we should throw an error on pg_start_backup() and pg_stop_backup if full_page_writes is off. Seems archive_command and full_page_writes can still be used if we are not in the process of doing a file system backup. In fact, could we have pg_start_backup() turn on full_page_writes and have pg_stop_backup turn it off, if postgresql.conf has it off. -- Bruce Momjian http://candle.pha.pa.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
