Re: [HACKERS] Proposal: Improve bitmap costing for lossy pages - Mailing list pgsql-hackers

Hi Dilip,

v6 patch:42 +   /*43 +    * Estimate number of hashtable entries we can have within
maxbytes. This44 +    * estimates the hash cost as sizeof(PagetableEntry).45 +    */46 +   nbuckets = maxbytes /47 +
  (sizeof(PagetableEntry) + sizeof(Pointer) + sizeof(Pointer));
 

It took me a little while to understand this calculation.  You have moved this
code from tbm_create(), but I think you should move the following
comment as well:

tidbitmap.c:276     /*277      * Estimate number of hashtable entries we can have within
maxbytes. This278      * estimates the hash cost as sizeof(PagetableEntry), which
is good enough279      * for our purpose.  Also count an extra Pointer per entry
for the arrays280      * created during iteration readout.281      */

Regards,
Amul


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