Re: WAL and commit_delay

* Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> [010217 14:50]:
> > * 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.
I've written swap files and such with:

dd if=/dev/zero of=SWAPFILE bs=512 count=204800

and all the blocks are allocated.

LER

>
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