| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Larry Rosenman <ler(at)lerctr(dot)org> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, vadim4o(at)email(dot)com |
| Subject: | Re: WAL and commit_delay |
| Date: | 2001-02-17 20:50:49 |
| Message-ID: | 200102172050.PAA03213@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
> * Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> [010217 14:46]:
> > > Right now the WAL preallocation code (XLogFileInit) is not good enough
> > > because it does lseek to the 16MB position and then writes 1 byte there.
> > > On an implementation that supports holes in files (which is most Unixen)
> > > that doesn't cause physical allocation of the intervening space. We'd
> > > have to actually write zeroes into all 16MB to ensure the space is
> > > allocated ... but that's just a couple more lines of code.
> >
> > Are OS's smart enough to not allocate zero-written blocks? Do we need
> > to write non-zeros?
> I don't believe so. writing Zeros is valid.
The reason I ask is because I know you get zeros when trying to read
data from a file with holes, so it seems some OS could actually drop
those blocks from storage.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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