On Tue, Dec 7, 2010 at 2:33 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: > Excerpts from Jon Nelson's message of 2010-12-07 15:25:47 -0500: >> On Tue, Dec 7, 2010 at 2:02 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: >> > Excerpts from Jon Nelson's message of 2010-12-07 14:34:40 -0500: >> >> On Tue, Dec 7, 2010 at 12:52 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: >> >> >> postgresql errors. Typically, header corruption but from the limited >> >> >> visibility I've had into this via strace, what I see is zeroed pages >> >> >> where there shouldn't be. >> >> > >> >> > This sounds a lot like a bug higher up than dm-crypt. ÂZeros tend to >> >> > come from some piece of code explicitly filling a page with zeros, and >> >> > that often happens in the corner cases for O_DIRECT and a few other >> >> > places in the filesystem. >> >> > >> >> > Have you tried triggering this with a regular block device? >> >> >> >> I just tried the whole set of tests, but with /dev/sdb directly (as >> >> ext4) without any crypt-y bits. >> >> It takes more iterations but out of 6 tests I had one failure: same >> >> type of thing, 'invalid page header in block ....'. >> >> >> >> I can't guarantee that it is a full-page of zeroes, just what I saw >> >> from the (limited) stracing I did. >> > >> > Fantastic. Now for our usual suspects: >> > >> > 1) Is postgres using O_DIRECT? ÂIf yes, please turn it off >> >> According to strace, O_DIRECT didn't show up once during the test. >> >> > 2) Is postgres allocating sparse files? ÂIf yes, please have it fully >> > allocate the file instead. >> >> That's a tough one. I don't think postgresql does that, but I'm not an >> expert here. >> >> > 3) Is postgres using preallocation (fallocate)? ÂIf yes, please have it >> > fully allocate the file instead >> >> As far as strace is concerned, postgreql is not using fallocate in >> this version. > > Well, the only other usual suspect would be mmap. ÂDoes the strace show > that you're using read/write for file IO or is it doing a lot of mmaps > on the files? I'm pretty sure postgresql uses regular file I/O and not mmap. -- Jon -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
