Re: Tuning threshold for BAS_BULKREAD (large tables)

Ron <ronljohnsonjr@xxxxxxxxx> · Tue, 22 Jan 2019 02:36:28 -0600



    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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