SET TRANSACTION * proposal

Continuing the thread about checkpointing. While I was browsing through
SQL standard documents I noticed that there are clauses like:

SET TRANSACTION {READ UNCOMMITED|READ COMMITED|READ
REPEATABLE|SERIALIZABLE}

I was wondering... If we have non-overwriting feature of postgres, we
would accomplish no-lock reads for at least first two isolation levels.

Also, by adding 'checkpointed' flag to each record we would allow for:
SET TRANSACTION READ CHECKPOINTED
(it's out of SQL Standard, but I couldn't find the right command)

During CHECKPOINT we would mark all the current records with
'checkpointed' flag. Also checkpointing would do VACUUM, so it would be
guaranteed that each checkpointed record would be the first in it's
modification chain.

Then for READ CHECKPOINTED transaction mode we would accomplish no-lock
reading which is especially usefull when you have to do a very long
statistical query on your data being constantly updated. Also, it would
be guaranteed that checkpointed data are consistent.

Is this hard to accomplish?

Mike

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add: Michal Mosiewicz * Bugaj 66 m.54 * 95-200 Pabianice * POLAND