We have recently discovered a problem with our slony-1 cluster of 8.1.19 installs. Specifically, we are unable to vacuum a table on the master node; vacuum always hangs on the same index of the same table. If we do a slony switchover and make the other node the master, then *it* will become unable to vacuum that index. Vacuum on the slave always works quickly and without issue. Vacuum does not hang anywhere else.

When we tried to strace the vacuuming backend, it appeared as if it was trying to acquire a lock, but pg_lock showed nothing unexpected for that index. We can also manually acquire an access exclusive lock on the offending table if we desire. FWIW, we have about 1,000 sessions, and while most of them are idle, we still average a couple hundred queries/s. The index in question is a simple unique btree over a column of type character(40).

Has anybody else experienced anything like this? We are hoping this problem magically goes away when we upgrade to 8.4 next month, but it would be great if we could solve it before then.

Thanks for any suggestions....

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