2018-07-17 22:13 GMT-03:00 Neto pr <netopr9@xxxxxxxxx>: > 2018-07-17 20:04 GMT-03:00 Mark Kirkwood <mark.kirkwood@xxxxxxxxxxxxxxx>: >> Ok, so dropping the cache is good. >> >> How are you ensuring that you have one test setup on the HDDs and one on the >> SSDs? i.e do you have 2 postgres instances? or are you using one instance >> with tablespaces to locate the relevant tables? If the 2nd case then you >> will get pollution of shared_buffers if you don't restart between the HHD >> and SSD tests. If you have 2 instances then you need to carefully check the >> parameters are set the same (and probably shut the HDD instance down when >> testing the SSD etc). >> > Dear Mark > To ensure that the test is honest and has the same configuration the > O.S. and also DBMS, my O.S. is installed on the SSD and DBMS as well. > I have an instance only of DBMS and two database. > - a database called tpch40gnorhdd with tablespace on the HDD disk. > - a database called tpch40gnorssd with tablespace on the SSD disk. > See below: > > postgres=# \l > List of databases > Name | Owner | Encoding | Collate | Ctype | > Access privileges > ---------------+----------+----------+-------------+-------------+----------------------- > postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | > template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | > =c/postgres + > | | | | | > postgres=CTc/postgres > template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | > =c/postgres + > | | | | | > postgres=CTc/postgres > tpch40gnorhdd | user1 | UTF8 | en_US.UTF-8 | en_US.UTF-8 | > tpch40gnorssd | user1 | UTF8 | en_US.UTF-8 | en_US.UTF-8 | > (5 rows) > > postgres=# > > After 7 query execution in a database tpch40gnorhdd I restart the DBMS > (/etc/init.d/pg101norssd restart and drop cache of the O.S.) and go to > execution test with the database tpch40gnorssd. > You think in this case there is pollution of shared_buffers? > Why do you think having O.S. on SSD is bad? Do you could explain better? > > Best regards > []`s Neto > +1 information about EVO SSD Samsung: Model: 850 Evo 500 GB SATA III 6Gb/s - http://www.samsung.com/semiconductor/minisite/ssd/product/consumer/850evo/ >> I can see a couple of things in your setup that might pessimize the SDD >> case: >> - you have OS on the SSD - if you tests make the system swap then this will >> wreck the SSD result >> - you have RAID 0 SSD...some of the cheaper ones slow down when you do this. >> maybe test with a single SSD >> >> regards >> Mark >> >> On 18/07/18 01:04, Neto pr wrote (note snippage): >> >>> (echo 3> / proc / sys / vm / drop_caches; >>> >>> discs: >>> - 2 units of Samsung Evo SSD 500 GB (mounted on ZERO RAID) >>> - 2 SATA 7500 Krpm HDD units - 1TB (mounted on ZERO RAID) >>> >>> - The Operating System and the Postgresql DBMS are installed on the SSD >>> disk. >>> >>> >>
