Re: Tuning threshold for BAS_BULKREAD (large tables)

On 1/22/19 1:35 AM, Jamison, Kirk wrote:
>
> Hi,
>
> I have a source code-related question on BufferAccessStrategyType
> BAS_BULKREAD.
>
> Currently, this access method is set internally to cache tables larger
> than 1/4 of shared_buffers.
>
> src/backend/access/heap/heapam.c:initscan()
>
>      if (!RelationUsesLocalBuffers(scan->rs_rd) &&
>
> scan->rs_nblocks > NBuffers / 4)
>
>         ...
>
>          /* During a rescan, keep the previous strategy object. */
>
>          if (scan->rs_strategy == NULL)
>
>    scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
>
> Users can tune their shared_buffers size, but not able to tune this component.
>
> I'm just wondering how it affects the current workload when the table size
> is larger than the database.
>

How can a subset of the database be larger than the database?

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