Re: Searching in varchar column having 100M records

On Fri, Jul 19, 2019 at 8:13 AM mayank rupareliya <[email protected]>
wrote:

> Well, you haven't shown us the execution plan, so it's hard to check why
> it did not help much and give you further advice.
>
>
> This is the latest query execution with explain after adding indexing on
> both columns.
>
> Aggregate  (cost=174173.57..174173.58 rows=1 width=8) (actual
> time=65087.657..65087.658 rows=1 loops=1)
>   ->  Bitmap Heap Scan on fields  (cost=1382.56..174042.61 rows=52386
> width=0) (actual time=160.340..65024.533 rows=31857 loops=1)
>         Recheck Cond: ((field)::text = 'Champlin'::text)
>         Heap Blocks: exact=31433
>         ->  Bitmap Index Scan on index_field  (cost=0.00..1369.46
> rows=52386 width=0) (actual time=125.078..125.079 rows=31857 loops=1)
>               Index Cond: ((field)::text = 'Champlin'::text)
> Planning Time: 8.595 ms
> Execution Time: 65093.508 ms
>
>>
>>

Are you on a solid state drive? If so, have you tried setting
effective_io_concurrency to 200 or 300 and checking performance? Given
nearly all of the execution time is doing a bitmap heap scan, I wonder
about adjusting this.

https://www.postgresql.org/docs/current/runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-ASYNC-BEHAVIOR
effective_io_concurrency
"The allowed range is 1 to 1000, or zero to disable issuance of
asynchronous I/O requests. Currently, this setting only affects bitmap heap
scans."
"The default is 1 on supported systems, otherwise 0. "