On Tue, 06 Jan 2026 at 16:23, Heikki Linnakangas <[email protected]> wrote: > On 30/12/2025 14:37, Andrey Borodin wrote: >> Hi hackers, >> Following up on the Discord discussion about the PROCLOCK hash table >> being >> a "weird allocator" that we never actually use for lookups - I took a stab at >> replacing it with a simpler partitioned free list approach as was suggested. >> I was doing this mostly to educate myself on Lock Manager internals. >> The current implementation uses LockMethodProcLockHash purely as an >> allocator. >> We never do hash lookups by key; we only allocate entries, link them to the >> lock's >> procLocks list, and free them later. Using a full hash table for this adds >> unnecessary complexity and maybe even overhead (I did not measure this). >> The attached patch replaces this with: >> - ProcLockArray: A fixed-size array of all PROCLOCK structs (allocated at >> startup) >> - ProcLockFreeList: Partitioned free lists, one per lock partition to reduce >> contention >> - ProcLockAlloc/Free: Simple push/pop operations on the free lists >> - PROCLOCK lookup: Linear traversal of lock->procLocks (see >> LockRefindAndRelease() >> and FastPathGetRelationLockEntry()) >> The last point bothers me most. It seems like this traversals are >> expected to be short. >> But I'm not 100% sure. > > Hmm, yeah the last point contradicts the premise that the hash table > is used purely as an allocator. It *is* used for lookups, and you're > replacing them with linear scans. That doesn't seem like an > improvement. > > - Heikki
I tested the patch on a Loongson 3C6000/D system with 128 vCPUs using BenchmarkSQL 5.0 (100 warehouses, 100 clients). Here are the results: | | tpmC | tpmTotal | |---------|-----------|-----------| | master | 248199.09 | 551387.46 | | | 243660.35 | 541902.31 | | | 244418.30 | 542867.57 | | patched | 247330.65 | 549949.25 | | | 242953.79 | 539620.65 | | | 237883.19 | 528491.66 | Not sure if this is useful, but throwing it out there. -- Regards, Japin Li ChengDu WenWu Information Technology Co., Ltd.
