Re: [HACKERS] WAL and commit_delay

[Bruce Momjian]

> 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?

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