Re: Poor Performance on Postgres 8.0

The random_page_cost value is same on both the versions, the only thing
difference between 7.4 version and 8 version is that 7.4 ver has 100k
less records. For, now i created index on numericvalue column on
attribute table and it used that index and it is much faster that way.
it came down to 24msec.

Also, i tried to see the matching id for squarefeet in attribute table
there are 800 some records in attribute table for 8 version and 700
something in 7.4 version.

Tom Lane wrote:

>Pallav Kalva <pkalva(at)deg(dot)cc> writes:
>
>
>>On 8
>> common | attribute | fknamestringid | 0 | 4
>>| 80 | {2524,2434,2530,2522,2525,2523,2527,2526,2574,2531} |
>>{0.219333,0.199333,0.076,0.0643333,0.0616667,0.05,0.0453333,0.042,0.04,0.0286667}
>>| {2437,2528,2529,2538,2539,2540,2554,2562,2575,2584,2637} | 0.0274016
>>
>>
>
>Given those stats, the planner is going to estimate that about 1/80th of
>the attribute table matches any particular fknamestringid, and that's
>what's driving it away from using the indexscan. I cannot tell whether
>there are indeed a couple of thousand rows joining to the 'squareFeet'
>string row (in which case the condition numericValue='775.0' must be
>really selective) or whether this is an outlier case that joins to just
>a few attribute rows.
>
>The slightly different stats values for 7.4 would have given it a
>slightly lower value for the cost of an indexscan by
>idx_attribute_fknamestringid, but certainly not as low as your original
>message shows. Perhaps you have some difference in parameter settings
>in your 7.4 installation --- most likely a lower random_page_cost.
>
> regards, tom lane
>
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