Re: Reorderbuffer crash during recovery

On 2019-Dec-27, vignesh C wrote:

> I felt amit solution also solves the problem. Attached patch has the
> fix based on the solution proposed.
> Thoughts?

This seems a sensible fix to me, though I didn't try to reproduce the
failure.

> @@ -2472,6 +2457,7 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
>  		}
>  
>  		ReorderBufferSerializeChange(rb, txn, fd, change);
> +		txn->final_lsn = change->lsn;
>  		dlist_delete(&change->node);
>  		ReorderBufferReturnChange(rb, change);

Should this be done insider ReorderBufferSerializeChange itself, instead
of in its caller?  Also, would it be sane to verify that the TXN
doesn't already have a newer final_lsn?  Maybe as an Assert.

> @@ -188,8 +188,7 @@ typedef struct ReorderBufferTXN
>  	 * * plain abort record
>  	 * * prepared transaction abort
>  	 * * error during decoding
> -	 * * for a crashed transaction, the LSN of the last change, regardless of
> -	 *   what it was.
> +	 * * last serialized lsn
>  	 * ----

I propose "for a transaction with serialized changes, the LSN of the
latest serialized one, unless one of the above cases."

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services