Re: logtape.c stats don't account for unused "prefetched" block numbers

On 2020-Sep-14, Peter Geoghegan wrote:

> On Fri, Sep 11, 2020 at 6:37 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > It would be awkward if we just used nBlocksWritten within
> > LogicalTapeSetBlocks() in the case where we didn't preallocate (or in
> > all cases). Not entirely sure what to do about that just yet.
>
> I guess that that's the logical thing to do, as in the attached patch.

I don't understand this patch. Or maybe I should say I don't understand
the code you're patching. Why isn't the correct answer *always*
nBlocksWritten? The comment in LogicalTapeSet says:

"nBlocksWritten is the size of the underlying file, in BLCKSZ blocks."

so if LogicalTapeSetBlocks wants to do what its comment says, that is,

"Obtain total disk space currently used by a LogicalTapeSet, in blocks."

then it seems like they're an exact match. Either that, or more than
zero of those comments are lying.

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Álvaro Herrera https://www.2ndQuadrant.com/
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