| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: changeset generation v5-01 - Patches & git tree |
| Date: | 2013-06-28 15:22:09 |
| Message-ID: | CA+TgmobiGzewn6g4gsJnVmR_s4G1i0qRhT8o3bxoWbdyjcW7GQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Jun 28, 2013 at 10:49 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert's idea sounds fairly reasonable to me; another 4 bytes per
> insert/update/delete WAL entry isn't that big a deal, ...
How big a deal is it? This is a serious question, because I don't
know. Let's suppose that the average size of an XLOG_HEAP_INSERT
record is 100 bytes. Then if we add 4 bytes, isn't that a 4%
overhead? And doesn't that seem significant?
I'm just talking out of my rear end here because I don't know what the
real numbers are, but it's far from obvious to me that there's any
free lunch here. That having been said, just because indexing
relfilenode or adding relfilenodes to WAL records is expensive doesn't
mean we shouldn't do it. But I think we need to know the price tag
before we can judge whether to make the purchase.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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