Re: [PATCH v4] technical doc: add a design doc for hash function transition

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 4, 2017, 01:44 UTC
Message-ID: <xmqqefqjheky.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170928044320.GA84719@aiede.mtv.corp.google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 8 quoted lines

> +Alternatives considered
> +-----------------------
> +Upgrading everyone working on a particular project on a flag day
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ...
> +Using hash functions in parallel
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ...

Good that we are not doing these ;-)

Show 7 quoted lines

> +Lazily populated translation table
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +Some of the work of building the translation table could be deferred to
> +push time, but that would significantly complicate and slow down pushes.
> +Calculating the sha1-name at object creation time at the same time it is
> +being streamed to disk and having its newhash-name calculated should be
> +an acceptable cost.

And the version described in the body of the document hopefully would be simpler. It certainly would be, when SHA-1 content and NewHash content are the same (i.e. blob).

THanks.