Re: LWLock contention: I think I understand the problem - Mailing list pgsql-hackers

  Tom Lane wrote:

>Attached is a modification that prevents additional waiters from being
>released until the first releasee has a chance to run and acquire the
>lock.  Would you try this and see if it's better or not in your test
>cases?  It doesn't seem to help on a single CPU, but maybe on multiple
>CPUs it'll make a difference.
>
Here are some results for Linux 2.2 on a Dual PentiumPro 200MHz, SCSI
disks and way too litte RAM
(just 128MB). I observed the loadavg. with the three different 7.2
versions and 50 clients, without patch
the load stayed low (2-3), with patch no1 very high (12-14) and with
patch no2 between the two others
(6-8). Any of the patches seem to be a big win with the second version
being slightly better. I could run
benchmarks on 7.1 if that would be interesting. I used the same
benchmark database with a
VACUUM FULL between each version of the backend tested. I also re-run
some of the tests on the same
database after I tested all loads on the different versions, and numbers
stayed very simmilar (difference:
 0.1-0.3 tps).

Best regrds
    Fredrik Estreen

--------------------------------------
7.2 CVS without patch
--------------------------------------
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 1
number of transactions per client: 1000
number of transactions actually processed: 1000/1000
tps = 16.169579(including connections establishing)
tps = 16.180891(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 2
number of transactions per client: 1000
number of transactions actually processed: 2000/2000
tps = 17.392394(including connections establishing)
tps = 17.404734(excluding connections establishing)
scaling factor: 50
transaction type: TPC-B (sort of)
number of clients: 5
number of transactions per client: 1000
number of transactions actually processed: 5000/5000
tps = 18.648499(including connections establishing)
tps = 18.661991(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 10
number of transactions per client: 1000
number of transactions actually processed: 10000/10000
tps = 15.405974(including connections establishing)
tps = 15.416244(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 25
number of transactions per client: 1000
number of transactions actually processed: 25000/25000
tps = 10.421300(including connections establishing)
tps = 10.425750(excluding connections establishing)
scaling factor: 50
number of clients: 50
number of transactions per client: 1000
number of transactions actually processed: 50000/50000
tps = 5.370482(including connections establishing)
tps = 5.371573(excluding connections establishing)

-------------------------------------
7.2 CVS with patch no1
--------------------------------------
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 1
number of transactions per client: 1000
number of transactions actually processed: 1000/1000
tps = 15.614858(including connections establishing)
tps = 15.625053(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 2
number of transactions per client: 1000
number of transactions actually processed: 2000/2000
tps = 18.165989(including connections establishing)
tps = 18.179211(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 5
number of transactions per client: 1000
number of transactions actually processed: 5000/5000
tps = 18.979070(including connections establishing)
tps = 18.993031(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 10
number of transactions per client: 1000
number of transactions actually processed: 10000/10000
tps = 19.809421(including connections establishing)
tps = 19.836396(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 25
number of transactions per client: 1000
number of transactions actually processed: 25000/25000
tps = 19.927333(including connections establishing)
tps = 19.942641(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 50
number of transactions per client: 1000
number of transactions actually processed: 50000/50000
tps = 16.888624(including connections establishing)
tps = 16.900136(excluding connections establishing)

--------------------------------------
7.2 CVS with patch no 2
--------------------------------------
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 1
number of transactions per client: 1000
number of transactions actually processed: 1000/1000
tps = 16.653249(including connections establishing)
tps = 16.664507(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 2
number of transactions per client: 1000
number of transactions actually processed: 2000/2000
tps = 18.773602(including connections establishing)
tps = 18.787637(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 5
number of transactions per client: 1000
number of transactions actually processed: 5000/5000
tps = 19.325495(including connections establishing)
tps = 19.339827(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 10
number of transactions per client: 1000
number of transactions actually processed: 10000/10000
tps = 20.251957(including connections establishing)
tps = 20.267558(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 25
number of transactions per client: 1000
number of transactions actually processed: 25000/25000
tps = 20.466319(including connections establishing)
tps = 20.482390(excluding connections establishing)
transaction type: TPC-B (sort of)
scaling factor: 50
number of clients: 50
number of transactions per client: 1000
number of transactions actually processed: 50000/50000
tps = 17.742367(including connections establishing)
tps = 17.754473(excluding connections establishing)