Re: Improving connection scalability: GetSnapshotData()

On Tue, Apr 7, 2020 at 1:51 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > ComputedHorizons seems like a fairly generic name. I think there's
> > some relationship between InvisibleToEveryoneState and
> > ComputedHorizons that should be brought out more clearly by the naming
> > and the comments.
>
> I don't like the naming of ComputedHorizons, ComputeTransactionHorizons
> much... But I find it hard to come up with something that's meaningfully
> better.

It would help to stick XID in there, like ComputedXIDHorizons. What I
find really baffling is that you seem to have two structures in the
same file that have essentially the same purpose, but the second one
(ComputedHorizons) has a lot more stuff in it. I can't understand why.

> What's the inconsistency? The dropped replication_ vs dropped FullXid
> postfix?

Yeah, just having the member names be randomly different between the
structs. Really harms greppability.

> > Generally, heap_prune_satisfies_vacuum looks pretty good. The
> > limited_oldest_committed naming is confusing, but the comments make it
> > a lot clearer.
>
> I didn't like _committed much either. But couldn't come up with
> something short. _relied_upon?

oldSnapshotLimitUsed or old_snapshot_limit_used, like currentCommandIdUsed?

> It's just adjusting for the changed name of latestCompletedXid to
> latestCompletedFullXid, as part of widening it to 64bits. I'm not
> really a fan of adding that to the variable name, but surrounding code
> already did it (cf VariableCache->nextFullXid), so I thought I'd follow
> suit.

Oops, that was me misreading the diff. Sorry for the noise.

--
Robert Haas
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