On Wed, Apr 3, 2024 at 10:04 PM Pavel Borisov <pashkin.e...@gmail.com> wrote: > On Wed, 3 Apr 2024 at 22:18, Alexander Korotkov <aekorot...@gmail.com> wrote: >> >> On Wed, Apr 3, 2024 at 7:55 PM Alvaro Herrera <alvhe...@alvh.no-ip.org> >> wrote: >> > >> > On 2024-Apr-03, Alexander Korotkov wrote: >> > >> > > Regarding the shmem data structure for LSN waiters. I didn't pick >> > > LWLock or ConditionVariable, because I needed the ability to wake up >> > > only those waiters whose LSN is already replayed. In my experience >> > > waking up a process is way slower than scanning a short flat array. >> > >> > I agree, but I think that's unrelated to what I was saying, which is >> > just the patch I attach here. >> >> Oh, sorry for the confusion. I'd re-read your message. Indeed you >> meant this very clearly! >> >> I'm good with the patch. Attached revision contains a bit of a commit >> message. >> >> > > However, I agree that when the number of waiters is very high and flat >> > > array may become a problem. It seems that the pairing heap is not >> > > hard to use for shmem structures. The only memory allocation call in >> > > paritingheap.c is in pairingheap_allocate(). So, it's only needed to >> > > be able to initialize the pairing heap in-place, and it will be fine >> > > for shmem. >> > >> > Ok. >> > >> > With the code as it stands today, everything in WaitLSNState apart from >> > the pairing heap is accessed without any locking. I think this is at >> > least partly OK because each backend only accesses its own entry; but it >> > deserves a comment. Or maybe something more, because WaitLSNSetLatches >> > does modify the entry for other backends. (Admittedly, this could only >> > happens for backends that are already sleeping, and it only happens >> > with the lock acquired, so it's probably okay. But clearly it deserves >> > a comment.) >> >> Please, check 0002 patch attached. I found it easier to move two >> assignments we previously moved out of lock, into the lock; then claim >> WaitLSNState.procInfos is also protected by WaitLSNLock. > > Could you re-attach 0002. Seems it failed to attach to the previous message.
I actually forgot both! ------ Regards, Alexander Korotkov
v2-0001-Use-an-LWLock-instead-of-a-spinlock-in-waitlsn.c.patch
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v2-0002-Clarify-what-is-protected-by-WaitLSNLock.patch
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