Subject: Re: [RFC] Introducing different handling for small/large transactions

From: Junio C Hamano <[email-masked]>
Date: Thu, 15 Jan 2015 15:34:19 -0800

Stefan Beller <[email-masked]> writes:

> In ref_transaction_commit
> 	* commit the .lock file to its destination
> 	* in case this is a deletion:
> 		* remove the loose ref
> 		* and repack the packed refs file if necessary

Don't you need to repack and then remove the loose one, though?
Otherwise you would expose a stale packed ref in the middle to the
other readers, no?

> The larger transactions would be handled differently by relying
> on the packed refs file:
> In ref_transaction_update:
> 	* detect if we transition to a large transaction
> 	  (by having more than one entry in transaction->updates)
> 	  if so:
> 		* Pack all currently existing refs into the packed
> 		  refs file, commit the packed refs file and delete
> 		  all loose refs. This will avoid (d/f) conflicts.
>
> 		* Keep the packed-refs file locked and move the first
> 		  transaction update into the packed-refs.lock file
>
> 	* Any update(delete, create, update) is put into the locked
> 	  packed refs file.

I am not sure if you mean (a) keep updates only in-core, to be
flushed at the commit time, or (b) each and every update in the
large transaction results in rewriting the entire packed-refs.lock
file, only to be renamed to the final name at the commit time.
I am hoping it would be the former.

> 	* Additionally we need to obtain the .lock for the loose refs
> 	  file to keep guarantees, though we should close the file
> 	  descriptor as we don't wand to run out of file descriptors.

Yes, this last point is important.