On Wed, Sep 14, 2016 at 5:45 AM, Pavan Deolasee
<pavan.deola...@gmail.com> wrote:
> Another interesting bit about these small tables is that the largest used
> offset for these tables never went beyond 291 which is the value of
> MaxHeapTuplesPerPage. I don't know if there is something that prevents
> inserting more than  MaxHeapTuplesPerPage offsets per heap page and I don't
> know at this point if this gives us upper limit for bits per page (may be it
> does).

>From PageAddItemExtended:

    /* Reject placing items beyond heap boundary, if heap */
    if ((flags & PAI_IS_HEAP) != 0 && offsetNumber > MaxHeapTuplesPerPage)
        elog(WARNING, "can't put more than MaxHeapTuplesPerPage items
in a heap page");
        return InvalidOffsetNumber;

Also see the comment where MaxHeapTuplesPerPage is defined:

 * Note: with HOT, there could theoretically be more line pointers (not actual
 * tuples) than this on a heap page.  However we constrain the number of line
 * pointers to this anyway, to avoid excessive line-pointer bloat and not
 * require increases in the size of work arrays.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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