On Sat, Mar 7, 2020 at 9:57 AM Dilip Kumar <dilipbal...@gmail.com> wrote:
> On Fri, Mar 6, 2020 at 9:47 AM Amit Kapila <amit.kapil...@gmail.com> > wrote: > > > > On Thu, Mar 5, 2020 at 1:54 PM Dilip Kumar <dilipbal...@gmail.com> > wrote: > > > > > > On Thu, Mar 5, 2020 at 12:15 PM Amit Kapila <amit.kapil...@gmail.com> > wrote: > > > > > > > > > > > > 5. I have also tried to think of another way to check if we already > > > > hold lock type LOCKTAG_RELATION_EXTEND, but couldn't come up with a > > > > cheaper way than this. Basically, I think if we traverse the > > > > MyProc->myProcLocks queue, we will get this information, but that > > > > doesn't seem much cheaper than this. > > > > > > I think we can maintain a flag (rel_extlock_held). And, we can set > > > that true in LockRelationForExtension, > > > ConditionalLockRelationForExtension functions and we can reset it in > > > UnlockRelationForExtension or in the error path e.g. LockReleaseAll. > > > > > > > I think if we reset it in LockReleaseAll during the error path, then > > we need to find a way to reset it during LockReleaseCurrentOwner as > > that is called during Subtransaction Abort which can be tricky as we > > don't know if it belongs to the current owner. How about resetting in > > Abort(Sub)Transaction and CommitTransaction after we release locks via > > ResourceOwnerRelease. > > I think instead of the flag we need to keep the counter because we can > acquire the same relation extension lock multiple times. So > basically, every time we acquire the lock we can increment the counter > and while releasing we can decrement it. During an error path, I > think it is fine to set it to 0 in CommitTransaction/AbortTransaction. > But, I am not sure that we can set to 0 or decrement it in > AbortSubTransaction because we are not sure whether we have acquired > the lock under this subtransaction or not. > > Having said that, I think there should not be any case that we are > starting the sub-transaction while holding the relation extension > lock. > Right, this is exactly the point. I think we can mention this in comments to make it clear why setting it to zero is fine during subtransaction abort. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
