Re: [HACKERS] snapbuild woes

On 25/04/17 00:59, Andres Freund wrote:
> Hi,
> 
> On 2017-04-15 05:18:49 +0200, Petr Jelinek wrote:
>> Hi, here is updated patch (details inline).
> 
> I'm not yet all that happy, sorry:
> 
> Looking at 0001:
> - GetOldestSafeDecodingTransactionId() only guarantees to return an xid
>   safe for decoding (note how procArray->replication_slot_catalog_xmin
>   is checked), not one for the initial snapshot - so afaics this whole
>   exercise doesn't guarantee much so far.
> - A later commit introduces need_full_snapshot as a
>   CreateInitDecodingContext, but you don't use it, not here.  That seems
>   wrong.

Ah yeah looks like that optimization is useful even here.

> - I remain unhappy with the handling of the reset of effective_xmin in
>   FreeDecodingContext(). What if we ERROR/FATAL out before that happens?
> 

Oh your problem was that I did it in FreeDecodingContext() instead of
slot release, that I didn't get, yeah sure it's possibly better place.

> What do you think about something like the attached?  I've not yet
> tested it any way except running the regression tests.
> 

> -    if (!already_locked)
> -        LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
> +    LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);

Don't really understand this change much, but otherwise the patch looks
good to me.

--  Petr Jelinek                  http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training &
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