
   Transaction id is incremented even in sql queries like
"select"  which does not change the state of database, is it not
unnecesary?.




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Wed, 15 Aug 2001 05:56:22 +0000
"maruthi maruthi" <maruthi49@hotmail.com>
Transaction id inrement
"maruthi maruthi" <maruthi49@hotmail.com> writes:
>    Transaction id is incremented even in sql queries like
> "select"  which does not change the state of database, is it not
> unnecesary?.

No, it's not unnecessary.  Every DB operation has to have a transaction
ID; what's more, we have to assign one long before we have any idea
whether the transaction will prove to be read-only.

It's at least theoretically possible that we could recycle the
transaction ID of a completed transaction that's proven to be read-only,
but the bookkeeping involved would be far more trouble than it's worth.
Not least because it would break MVCC assumptions about transactions
starting in sequence number order.

			regards, tom lane

Mon, 20 Aug 2001 11:22:45 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Transaction id inrement 