On Tue, Nov 27, 2018 at 7:45 AM Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > On 2018-Nov-26, Jakub Glapa wrote: > > Justin thanks for the information! > > I'm running Ubuntu 16.04. > > I'll try to prepare for the next crash. > > Couldn't find anything this time. > > As I recall, the appport stuff in Ubuntu is terrible ... I've seen it > take 40 minutes to write the crash dump to disk, during which the > database was "down". I don't know why it is so slow (it's a rather > silly python script that apparently processes the core dump one byte at > a time, and you can imagine that with a few gigabytes of shared memory > that takes a while). Anyway my recommendation was to *remove* that > stuff from the server and make sure the core file is saved by normal > means.
Thanks for CC-ing me. I didn't see this thread earlier because I'm not subscribed to -performance. Let's move it over to -hackers since it looks like it's going to be a debugging exercise. So, reading through the thread[1], I think there might be two independent problems here: 1. Jakub has a many-partition Parallel Bitmap Heap Scan query that segfaults when run with max_parallel_workers = 0. That sounds suspiciously like an instance of a class of bug we've run into before. We planned a parallel query, but were unable to launch one due to lack of DSM slots or process slots, so we run the parallel plan in a kind of degraded non-parallel mode that needs to cope with various pointers into shared memory being NULL. A back trace from a core file should hopefully make it very obvious what's going on. 2. The same query when run in real parallel query mode occasionally reaches an error "dsa_allocate could not find 7 free pages", which should not happen. This is on 10.6, so it has the commit "Fix segment_bins corruption in dsa.c.". Hmm. I will see if I can come up with a many-partition torture test reproducer for this. [1] https://www.postgresql.org/message-id/flat/CAJk1zg10iCNsxFvQ4pgKe1B0rdjNG9iELA7AzLXjXnQm5T%3DKzQ%40mail.gmail.com -- Thomas Munro http://www.enterprisedb.com
