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.
