Re: Index Scans become Seq Scans after VACUUM ANALYSE - Mailing list pgsql-hackers

From Michael Loftis
Subject Re: Index Scans become Seq Scans after VACUUM ANALYSE
Date
Msg-id 3CBEDB89.3080403@wgops.com
Whole thread Raw
In response to Re: Index Scans become Seq Scans after VACUUM ANALYSE  (Bruce Momjian <pgman@candle.pha.pa.us>)
Responses Re: Index Scans become Seq Scans after VACUUM ANALYSE  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
Somethings wrong with the random numbers from the sun... re-run them, 
that first sample is insane....  Caching looks like it's affecctign your 
results alot...

Mark Pritchard wrote:

>I threw together the attached program (compiles fine with gcc 2.95.2 on
>Solaris 2.6 and egcs-2.91.66 on RedHat Linux 6.2) and ran it a few
>times. Data is below. Usual disclaimers about hastily written code etc
>:)
>
>Machine = ghoul (generic intel, 384mb ram, dual p3-800, ide disk running
>dma)
>
>Sequential
>Bytes Read    Time    Bytes / Sec
>536870912       27.14   19783933.74
>536870912       27.14   19783990.60
>536870912       27.11   19801872.14
>536870912       26.92   19942928.41
>536870912       27.31   19657408.43
>                        19794026.66 (avg)
>
>Random        
>Bytes Read    Time    Bytes / Sec
>1073741824      519.57  2066589.21
>1073741824      517.78  2073751.44
>1073741824      516.92  2077193.23
>1073741824      513.18  2092333.29
>1073741824      510.68  2102579.88
>                        2082489.41 (avg)
>
>Machine = jedi (Sun E420, 3gb ram, dual 400s, test on single scsi disk)
>
>Sequential        
>Bytes Read    Time    Bytes / Sec
>2097152000      65.19   32167675.28
>2097152000      65.22   32154114.65
>2097152000      65.16   32182561.99
>2097152000      65.12   32206105.12
>2097152000      64.67   32429463.26
>                        32227984.06 (avg)
>
>Random        
>Bytes Read    Time    Bytes / Sec
>4194304000      1522.22 2755394.79
>4194304000      278.18  15077622.05
>4194304000      91.43   45874730.07
>4194304000      61.43   68273795.19
>4194304000      54.55   76890231.51
>                        41774354.72
>
>If I interpret Tom's "divide" instruction correctly, is that a factor of
>10 on the linux box?
>




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