On 2014-02-14 20:46:01 +0000, Greg Stark wrote: > Going over this I think this is still a potential issue: > > On 31 Jan 2014 15:56, "Andres Freund" <and...@2ndquadrant.com> wrote: > > > > > I am not sure that explains the issue, but I think the redo action for > > truncation is not safe across crashes. A XLOG_SMGR_TRUNCATE will just > > do a smgrtruncate() (and then mdtruncate) which will iterate over the > > segments starting at 0 till mdnblocks()/segment_size and *truncate* but > > not delete individual segment files that are not needed anymore, right? > > If we crash in the midst of that a new mdtruncate() will be issued, but > > it will get a shorter value back from mdnblocks(). > > > > Am I missing something? > > > > I'm not too familiar with md.c but my reading of the code is that we > truncate the files in reverse order?
That's what I had assumed as well, but it doesn't look that way: v = mdopen(reln, forknum, EXTENSION_FAIL); priorblocks = 0; /* <- initial value */ while (v != NULL) { MdfdVec *ov = v; if (priorblocks > nblocks) { /* truncate entire segment */ } else if (priorblocks + ((BlockNumber) RELSEG_SIZE) > nblocks) { /* truncate entire segment */ } else { /* nothing to do, all needed */ } priorblocks += RELSEG_SIZE; } So, according to that we start at segment 0, right? Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers