| From: | amul sul <sulamul(at)gmail(dot)com> |
|---|---|
| To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Cc: | Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposal: Improve bitmap costing for lossy pages |
| Date: | 2017-11-09 08:55:24 |
| Message-ID: | CAAJ_b94+TAaBj4VeYGuEJUGdQSV1X4KfLhNR8pqrJJZ1Rc=aww@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi Dilip,
v6 patch:
42 + /*
43 + * Estimate number of hashtable entries we can have within
maxbytes. This
44 + * 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. This
278 * estimates the hash cost as sizeof(PagetableEntry), which
is good enough
279 * for our purpose. Also count an extra Pointer per entry
for the arrays
280 * created during iteration readout.
281 */
Regards,
Amul
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