Laurenz Albe <laurenz.albe@xxxxxxxxxxx> writes: > On Thu, 2020-08-27 at 10:10 +0530, Hemil Ruparel wrote: >> I was playing with Advisory locks. I opened three connections to the database And obtained >> a lock with the same key. I noticed that the locks were obtained in the order of requests. >> I was wondering whether the locks are guaranteed to be First Come First Serve and can this >> behaviour be relied upon. > Yes - lock requests that block are queued, with later lock requests queued behind previous > ones. Once a lock gets free, the first in line gets it. > This is the same for all heavyweight locks in PostgreSQL. There is an exception: the queue order will be rearranged if we find that doing so is necessary to avoid a deadlock failure. See src/backend/storage/lmgr/README regards, tom lane
