Jeff Janes escribió:
> On Thu, Feb 7, 2013 at 10:09 AM, Pavan Deolasee
> <[email protected]> wrote:
> >
> > Right. I don't have the database handy at this moment, but earlier in
> > the day I ran some queries against it and found that most of the
> > duplicates which are not accessible via indexes have xmin very close
> > to 2100345903. In fact, many of them are from a consecutive range.
>
> Does anyone have suggestions on how to hack the system to make it
> fast-forward the current transaction id? It would certainly make
> testing this kind of thing faster if I could make transaction id
> increment by 100 each time a new one is generated. Then wrap-around
> could be approached in minutes rather than hours.
I can reproduce the problem in a few minutes with the attached.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index 64537d0..9513faf 100644
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -159,16 +159,25 @@ GetNewTransactionId(bool isSubXact)
*
* Extend pg_subtrans too.
*/
- ExtendCLOG(xid);
- ExtendSUBTRANS(xid);
+ {
+ int incr = pg_lrand48() & 0x7FF;
- /*
- * Now advance the nextXid counter. This must not happen until after we
- * have successfully completed ExtendCLOG() --- if that routine fails, we
- * want the next incoming transaction to try it again. We cannot assign
- * more XIDs until there is CLOG space for them.
- */
- TransactionIdAdvance(ShmemVariableCache->nextXid);
+ for (; incr > 0; incr--)
+ {
+ xid = ShmemVariableCache->nextXid;
+
+ ExtendCLOG(xid);
+ ExtendSUBTRANS(xid);
+
+ /*
+ * Now advance the nextXid counter. This must not happen until after we
+ * have successfully completed ExtendCLOG() --- if that routine fails, we
+ * want the next incoming transaction to try it again. We cannot assign
+ * more XIDs until there is CLOG space for them.
+ */
+ TransactionIdAdvance(ShmemVariableCache->nextXid);
+ }
+ }
/*
* We must store the new XID into the shared ProcArray before releasing
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