| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Optimizing TransactionIdIsCurrentTransactionId() |
| Date: | 2019-12-19 19:27:01 |
| Message-ID: | CA+TgmoZttdAwKy22JSSdJuvu-qieZ-NW_ivqJXfRYCumMFc1Vg@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Wed, Dec 18, 2019 at 5:07 AM Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> TransactionIdIsCurrentTransactionId() doesn't seem to be well optimized for the case when an xid has not yet been assigned, so for read only transactions.
>
> A patch for this is attached.
It might be an idea to first call TransactionIdIsNormal(xid), then
GetTopTransactionIdIfAny(), then TransactionIdIsNormal(topxid), so
that we don't bother with GetTopTransactionIdIfAny() when
!TransactionIdIsNormal(xid).
But it's also not clear to me whether this is actually a win. You're
dong an extra TransactionIdIsNormal() test to sometimes avoid a
GetTopTransactionIdIfAny() test. TransactionIdIsNormal() is pretty
cheap, but GetTopTransactionIdIfAny() isn't all that expensive either,
and adding more branches costs something.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Jeremy Schneider | 2019-12-19 19:28:55 | Re: Proposal: Global Index |
| Previous Message | Juan José Santamaría Flecha | 2019-12-19 19:09:45 | Re: Clean up some old cruft related to Windows |