Re: tracking commit timestamps

Robert Haas wrote:

> I think the key question here is the time for which the data needs to
> be retained. 2^32 of anything is a lot, but why keep around that
> number of records rather than more (after all, we have epochs to
> distinguish one use of a given txid from another) or fewer?

The problem is not how much data we retain; is about how much data we
can address. We must be able to address the data for transaction with
xid=2^32-1, even if you only retain the 1000 most recent transactions.
In fact, we already only retain data back to RecentXmin, if I recall
correctly. All slru.c users work that way.

Back when pg_multixact/members had the 5-char issue, I came up with a
patch that had each slru.c user declare how many chars maximum were the
filenames. I didn't push further with that because there was an issue
with it, I don't remember what it was offhand (but I don't think I
posted it). But this is only needed so that the filenames are all equal
width, which is mostly cosmetical; the rest of the module works fine
with 4- or 5-char filenames, and can be trivially expanded to support 6
or more.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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