2018-01-15 15:32 GMT-03:00 Georg H. <geor...@silentrunner.de>:

> 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.


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