| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: logtape.c stats don't account for unused "prefetched" block numbers |
| Date: | 2020-09-14 22:23:59 |
| Message-ID: | 20200914222359.GA6834@alvherre.pgsql |
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| Lists: | pgsql-hackers |
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.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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