Re: Usage of epoch in txid_current

On Thu, Mar 28, 2019 at 1:30 AM Thomas Munro <thomas.munro@gmail.com> wrote:

On Thu, Mar 28, 2019 at 1:48 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> Once we have the FullTransactionId type and basic macros in place, I'm
> sure we could tidy up a bunch of code by using them.

Thanks for the reviews!  Pushed.

I think that this might be broken.

We have this change:

@@ -73,7 +75,8 @@ GetNewTransactionId(bool isSubXact)

 

    LWLockAcquire(XidGenLock, LW_EXCLUSIVE);

 

-   xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);

+   full_xid = ShmemVariableCache->nextFullXid;

+   xid = XidFromFullTransactionId(full_xid);

But then later on in an little-used code path around line 164:

        /* Re-acquire lock and start over */

        LWLockAcquire(XidGenLock, LW_EXCLUSIVE);

        xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);

full_xid does not get updated, but then later on full_xid gets returned in lieu of xid.

Is there a reason that this is OK?