I also tried explain but found nothing special:
explain select * from data_table where thing_id in
(164438,112478,102941,112377,164442,181764,104028);
QUERY PLAN
-------------------------------------------------------------------------------------------------------
Bitmap Heap Scan on data_table (cost=31.75..579.10 rows=141 width=53)
Recheck Cond: (thing_id = ANY
('{164438,112478,102941,112377,164442,181764,104028}'::bigint[]))
-> Bitmap Index Scan on idx_data_table (cost=0.00..31.71 rows=141 width=0)
Index Cond: (thing_id = ANY
('{164438,112478,102941,112377,164442,181764,104028}'::bigint[]))
On Thu, Jan 12, 2012 at 4:47 PM, Yan Chunlu <springrider@gmail.com> wrote:
> I am transforming a db with millions records to anther schema. for
> some reason I need to select the records using IN (xx,xx).
>
> the ids in the IN was about 1000 recored every time, but I found the
> query was getting slow while the selection moving on.
>
> the shared buffer is 2048M. and the cpu and io usage is as normal.
>
> But while I am processing a smaller db on another machine, which only
> has the default 24MB, the selection went very smooth.
>
>
> here is the logs:
>
> start... 0 limit:1000
> selection time: 0.140721082687
> sort_options
> msgtime
> start... 1000 limit:1000
> selection time: 0.122759103775
> start... 2000 limit:1000
> selection time: 0.150802850723
> start... 3000 limit:1000
> selection time: 0.173918008804
> start... 4000 limit:1000
> selection time: 0.212812900543
> start... 5000 limit:1000
> selection time: 0.255054950714
> start... 6000 limit:1000
> selection time: 0.230540037155
> start... 7000 limit:1000
> selection time: 0.24426317215
> start... 8000 limit:1000
> selection time: 0.326669931412
> start... 9000 limit:1000
> selection time: 0.351358175278
> start... 10000 limit:1000
> selection time: 0.386382102966
> start... 11000 limit:1000
> selection time: 0.440491914749
> start... 12000 limit:1000
> selection time: 0.443608045578
> start... 13000 limit:1000
> selection time: 0.49751496315
> start... 14000 limit:1000
> selection time: 12.0050361156
> start... 15000 limit:1000
> selection time: 26.3596658707
>
> start... 16000 limit:1000
> selection time: 43.5269529819