On 2021-Jan-28, Alexey Kondratov wrote: > I have read more about lock levels and ShareLock should prevent any kind of > physical modification of indexes. We already hold ShareLock doing > find_all_inheritors(), which is higher than ShareUpdateExclusiveLock, so > using ShareLock seems to be safe here, but I will look on it closer.
You can look at lock.c where LockConflicts[] is; that would tell you that ShareLock indeed conflicts with ShareUpdateExclusiveLock ... but it does not conflict with itself! So it would be possible to have more than one process doing this thing at the same time, which surely makes no sense. I didn't look at the patch closely enough to understand why you're trying to do something like CLUSTER, VACUUM FULL or REINDEX without holding full AccessExclusiveLock on the relation. But do keep in mind that once you hold a lock on a relation, trying to grab a weaker lock afterwards is pretty pointless. -- Álvaro Herrera 39°49'30"S 73°17'W "E pur si muove" (Galileo Galilei)
