Re: WAL and commit_delay

> * Bruce Momjian <pgman@candle.pha.pa.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.

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