| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "maruthi maruthi" <maruthi49(at)hotmail(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Transaction id inrement |
| Date: | 2001-08-20 15:22:45 |
| Message-ID: | 8801.998320965@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
"maruthi maruthi" <maruthi49(at)hotmail(dot)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
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