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  1. Fix off-by-one error in txid_status().

  1. txid_status() off-by-one error

    Thomas Munro <thomas.munro@gmail.com> — 2019-03-27T06:55:57Z

    Hello hackers,

postgres=> select txid_status(txid_current() + 3);
ERROR:  transaction ID 627 is in the future
postgres=> select txid_status(txid_current() + 2);
ERROR:  transaction ID 627 is in the future
postgres=> select txid_status(txid_current() + 1);
 txid_status
-------------
 in progress
(1 row)

If you keep asking for txid_status(txid_current() + 1) in new
transactions, you eventually hit:

ERROR:  could not access status of transaction 32768
DETAIL:  Could not read from file "pg_xact/0000" at offset 8192: No error: 0.

I think the fix is:

--- a/src/backend/utils/adt/txid.c
+++ b/src/backend/utils/adt/txid.c
@@ -129,7 +129,7 @@ TransactionIdInRecentPast(uint64 xid_with_epoch,
TransactionId *extracted_xid)

        /* If the transaction ID is in the future, throw an error. */
        if (xid_epoch > now_epoch
-               || (xid_epoch == now_epoch && xid > now_epoch_last_xid))
+               || (xid_epoch == now_epoch && xid >= now_epoch_last_xid))
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("transaction ID %s is in the future",

-- 
Thomas Munro
https://enterprisedb.com

  2. Re: txid_status() off-by-one error

    Thomas Munro <thomas.munro@gmail.com> — 2019-03-27T08:49:45Z

    On Wed, Mar 27, 2019 at 7:55 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> If you keep asking for txid_status(txid_current() + 1) in new
> transactions, you eventually hit:
>
> ERROR:  could not access status of transaction 32768
> DETAIL:  Could not read from file "pg_xact/0000" at offset 8192: No error: 0.

> -               || (xid_epoch == now_epoch && xid > now_epoch_last_xid))
> +               || (xid_epoch == now_epoch && xid >= now_epoch_last_xid))

Pushed and back-patched, along with renaming of that variable, s/last/next/.

-- 
Thomas Munro
https://enterprisedb.com