Thread: Recovery on incomplete write
Hi all, I have wondered that md.c handles incomplete block(page)s correctly. Am I mistaken ? 1) _mdnblocks() takes the last incomplete block into account 2) mdextend() doesn't care about the existence of incomplete block(page)s. 3) In spite of 1)2),mdextend() does nothing when incomplete write occurs. Comments ? If I am right,I would provide a patch. Regards. Hiroshi Inoue Inoue@tpf.co.jp
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> I have wondered that md.c handles incomplete block(page)s
> correctly.
> Am I mistaken ?
I think you are right, and there may be some other trouble spots in that
file too. I remember thinking that the code depended heavily on never
having a partial block at the end of the file.
But is it worth fixing? The only way I can see for the file length
to become funny is if we run out of disk space part way through writing
a page, which seems unlikely...
regards, tom lane
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes: > > I have wondered that md.c handles incomplete block(page)s > > correctly. > > Am I mistaken ? > > I think you are right, and there may be some other trouble spots in that > file too. I remember thinking that the code depended heavily on never > having a partial block at the end of the file. > > But is it worth fixing? The only way I can see for the file length > to become funny is if we run out of disk space part way through writing > a page, which seems unlikely... > That is how he got started, the TODO item about running out of disk space causing corrupted databases. I think it needs a fix, if we can. -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
> -----Original Message----- > From: Bruce Momjian [mailto:maillist@candle.pha.pa.us] > Sent: Tuesday, September 28, 1999 11:54 PM > To: Tom Lane > Cc: Hiroshi Inoue; pgsql-hackers > Subject: Re: [HACKERS] Recovery on incomplete write > > > > "Hiroshi Inoue" <Inoue@tpf.co.jp> writes: > > > I have wondered that md.c handles incomplete block(page)s > > > correctly. > > > Am I mistaken ? > > > > I think you are right, and there may be some other trouble spots in that > > file too. I remember thinking that the code depended heavily on never > > having a partial block at the end of the file. > > > > But is it worth fixing? The only way I can see for the file length > > to become funny is if we run out of disk space part way through writing > > a page, which seems unlikely... > > > > That is how he got started, the TODO item about running out of disk > space causing corrupted databases. I think it needs a fix, if we can. > Maybe it isn't so difficult to fix. I would provide a patch. Regards. Hiroshi Inoue Inoue@tpf.co.jp
Bruce Momjian wrote: > > > > I think you are right, and there may be some other trouble spots in that > > file too. I remember thinking that the code depended heavily on never > > having a partial block at the end of the file. > > > > But is it worth fixing? The only way I can see for the file length > > to become funny is if we run out of disk space part way through writing > > a page, which seems unlikely... > > > > That is how he got started, the TODO item about running out of disk > space causing corrupted databases. I think it needs a fix, if we can. It does corrupt the database (happened twice to me last week, I'm using the current CVS version!). You can't even pg_dump the database - it stops in the middle of a line. And this happened just because some process went amok and stdout was written to a file. Christof