On Thu, 19 Dec 2019 at 19:27, Robert Haas <robertmh...@gmail.com> wrote:
> On Wed, Dec 18, 2019 at 5:07 AM Simon Riggs <si...@2ndquadrant.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. That's not the point of the patch. If the TopTransactionId is not assigned, we can leave the whole function more quickly, not just avoid a test. Read only transactions should have a fast path thru this function since they frequently read more data than write transactions. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Solutions for the Enterprise
