Tom Lane wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
I'm thinking of removing cmin and cmax, and keeping that information in
backend-private memory instead.
I don't believe you can remove *both*. What's been discussed is
removing one of them, by letting the field represent a lookup key for an
in-memory structure in the infrequent case that xmin and xmax are both
the current xact. You solve the table size problem by only having one
entry for each unique cmin/cmax pair in use.
That's another possibility, but removing both cmin and cmax has also
been discussed. It's also mentioned in the TODO item:
> One possible solution is to create a phantom cid which represents a
cmin/cmax pair and is stored in local memory. *Another idea is to store
both cmin and cmax only in local memory.*
Saving 4 bytes per tuple with the phantom cid is nice, but saving 8
bytes (assuming we get rid of xvac in the future, or overlay it with
xmin for example) is even better.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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