2018-01-15 17:55 GMT-02:00 Fernando Hevia <fhevia@xxxxxxxxx>: > > > 2018-01-15 15:32 GMT-03:00 Georg H. <georg-h@xxxxxxxxxxxxxxx>: >> >> >> Hello Neto >> >> Am 14.01.2018 um 21:44 schrieb Neto pr: >>> >>> Dear all >>> >>> Someone help me analyze the two execution plans below (Explain ANALYZE >>> used), is the query 9 of TPC-H benchmark [1]. >>> I'm using a server HP Intel Xeon 2.8GHz/4-core - Memory 8GB HDD SAS 320GB >>> 15 Krpm AND SSD Sansung EVO 500GB. >>> My DBMS parameters presents in postgresql.conf is default, but in SSD I >>> have changed random_page_cost = 1.0. >>> >> you are comparing a SAS Drive against a SATA SSD. Their interfaces serve a >> completely different bandwidth. >> While a SAS-3 device does 12 Gbit/s SATA-3 device is only able to >> transfer 6 Gbit/s (a current SAS-4 reaches 22.5 Gbit/s) >> Do a short research on SAS vs SATA and then use a SAS SSD for comparison >> :) > > > The query being all read operations both drives should perform somewhat > similarly. Therefore, either the SAS drive has some special sauce to it > (a.k.a very fast built-in cache) or there is something else going on these > systems. Otherwise he shouldn't be stressing the 6 Gbit/s interface limit > with a single drive, be that the SATA or the SAS drive. > > Neto, you have been suggested to provide a number of command outputs to know > more about your system. Testing the raw read throughput of both your drives > should be first on your list. > Guys, sorry for the Top Post, I forgot .... Fernando, I think the difference of 6 Gb/s to 12 Gb/s from SAS is what caused the difference in query execution time. Because looking at the execution plans and the cost estimate, I did not see many differences, in methods of access among other things. Regarding the query, none of them use indexes, since I did a first test without indexes. Do you think that if I compare the disk below HDD SAS that has a transfer rate of 6Gb/s equal to the SSD SATA 6Gb/s, do you think the SSD would be more agile in this case? HDD: HP 450GB 6G SAS 15K rpm LFF (3.5-inch) Part-Number: 652615-B21 Neto > Cheers. > > > >
