Jim C. Nasby wrote: > On Sun, Jul 30, 2006 at 11:44:44AM -0400, Tom Lane wrote: >> Alvaro Herrera <[EMAIL PROTECTED]> writes: >>> Stefan Kaltenbrunner wrote: >>>> FYI: lionfish just managed to hit that problem again: >>>> http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=lionfish&dt=2006-07-29%2023:30:06 >>> The test alter_table, which is on the same parallel group as limit (the >>> failing test), contains these lines: >>> ALTER INDEX onek_unique1 RENAME TO tmp_onek_unique1; >>> ALTER INDEX tmp_onek_unique1 RENAME TO onek_unique1; >> I bet Alvaro's spotted the problem. ALTER INDEX RENAME doesn't seem to >> take any lock on the index's parent table, only on the index itself. >> That means that a query on "onek" could be trying to read the pg_class >> entries for onek's indexes concurrently with someone trying to commit >> a pg_class update to rename an index. If the query manages to visit >> the new and old versions of the row in that order, and the commit >> happens between, *neither* of the versions would look valid. MVCC >> doesn't save us because this is all SnapshotNow. >> >> Not sure what to do about this. Trying to lock the parent table could >> easily be a cure-worse-than-the-disease, because it would create >> deadlock risks (we've already locked the index before we could look up >> and lock the parent). Thoughts? >> >> The path of least resistance might just be to not run these tests in >> parallel. The chance of this issue causing problems in the real world >> seems small. > > It doesn't seem that unusual to want to rename an index on a running > system, and it certainly doesn't seem like the kind of operation that > should pose a problem. So at the very least, we'd need a big fat warning > in the docs about how renaming an index could cause other queries in the > system to fail, and the error message needs to be improved.
it is my understanding that Tom is already tackling the underlying issue on a much more general base ... Stefan ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
