Re: Lock contention high

Hi
B-tree index used in the postgres environment
Checked on warehouse different values like 100,800,1600,2400 and 3200 with
virtual user 64
On different values(warehouse) the lock contention same i.e. approx 17% and
iostat usage is 30-40%

pg_Count_ware=100
-----------------
17.76% postgres postgres [.] LWLockAcquire
4.88% postgres postgres [.] _bt_compare
3.10% postgres postgres [.] LWLockRelease

pg_Count_ware=800(previously I used Warehouse 800)
--------------------------------------------
17.91% postgres postgres [.] LWLockAcquire
5.76% postgres postgres [.] _bt_compare
3.06% postgres postgres [.] LWLockRelease

pg_Count_ware_1600
-----------------
17.80% postgres postgres [.] LWLockAcquire
5.88% postgres postgres [.] _bt_compare
2.70% postgres postgres [.] LWLockRelease

pg_Count_ware_2400
------------------
17.77% postgres postgres [.] LWLockAcquire
6.01% postgres postgres [.] _bt_compare
2.71% postgres postgres [.] LWLockRelease

pg_Count_ware_3200
------------------
17.46% postgres postgres [.] LWLockAcquire
6.32% postgres postgres [.] _bt_compare
2.86% postgres postgres [.] hash_search_with_hash_value

1.Tired different values of lock management values in postgres.conf but it
not helped to reduce lock contention.
deadlock_timeout = 5s
max_locks_per_transaction = 64
max_pred_locks_per_transaction = 64
max_pred_locks_per_relation = -2

max_pred_locks_per_page = 2
2.Intention to check the postgreSQL scalability and performance or
throughput(TPC-C/TPC-H)
with HammerDB and pgbench with server configuration on tune
settings(postgresql.conf)-reduce lock contention
CPU's :256
Threadper core: 2
Core per socket: 64
Sockets: 2
NUMA node0 : 0-63,128-191
NUMA node1 : 64-127,192-255
RAM size :512GB
SSD :1TB

Ref link:
https://www.hammerdb.com/blog/uncategorized/hammerdb-best-practice-for-postgresql-performance-and-scalability/

On Thursday, October 14, 2021, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Tue, Oct 12, 2021 at 12:45 AM Ashkil Dighin <ashkildighin76(at)gmail(dot)com>
> wrote:
> > Lock contention observed high in PostgreSQLv13.3
> > The source code compiled with GNC(GCCv11.x)
> > PostgreSQL version: 13.3
> > Operating system: RHEL8.3
> > Kernel name:4.18.0-305.10.2.el8_4.x86_64
> > RAM Size:512GB
> > SSD: 1TB
> > The environment used IBM metal and test benchmark environment
> HammerDbv4.2
> > Test case :TPC-C
>
> You didn't say how many TPC-C warehouses you used. In my experience,
> people sometimes run TPC-C with relatively few, which will tend to
> result in extreme contention on certain B-Tree leaf pages. (My
> experiences are with BenchmarkSQL, but I can't imagine HammerDB is too
> much different.)
>
> Assuming that's the case here, for you, then it's not clear that you
> have a real problem. You're really not supposed to run the benchmark
> in that way, per the TPC-C spec, which strictly limits the number of
> transactions per minute per warehouse -- for better or worse, valid
> results generally require that you use lots of warehouses to get a
> very large database (think terabytes). If you run the benchmark with
> 100 warehouses or less, on a big server, then the contention you'll
> see will be out of all proportion to what you're ever likely to see in
> the real world.
>
> --
> Peter Geoghegan
>