From: Eric Sunshine <sunshine@sunshineco.com>
Date: Mon, 21 Dec 2015 07:06:59 GMT
Subject: Re: [PATCH 1/2] pack-revindex: drop hash table
Message-ID: <CAPig+cTD+qknnZ3rH7skcTxZA16AL0BPbLT5ZaJdwwu_d-i=Jw@mail.gmail.com>
In-Reply-To: <20151221061948.GA25763@sigill.intra.peff.net>

On Mon, Dec 21, 2015 at 1:19 AM, Jeff King <peff@peff.net> wrote:
> The main entry point to the pack-revindex code is
> find_pack_revindex(). This calls revindex_for_pack(), which
> lazily computes and caches the revindex for the pack.
>
> We store the cache in a very simple hash table. It's created
> by init_pack_revindex(), which inserts an entry for every
> packfile we know about, and we never grow or shrink the
> hash. If we ever need the revindex for a pack that isn't in
> the hash, we die() with an internal error.
>
> This can lead to a race, because we may load more packs
> after having called init_pack_revindex(). For example,
> imagine we have one process which needs to look at the
> revindex for a variety of objects (e.g., cat-file's
> "%(objectsize:disk)" format).  Simultaneously, git-gc is
> running, which is doing a `git repack -ad` is running. We
> might hit a sequence like:

Probably want to drop one of the "is running"s...