From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 15 Feb 2018 18:19:11 GMT
Subject: Re: [PATCH v3 04/14] commit-graph: implement write_commit_graph()
Message-ID: <xmqqinay9kv4.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <1518122258-157281-5-git-send-email-dstolee@microsoft.com>

Derrick Stolee <stolee@gmail.com> writes:

> +struct packed_oid_list {
> +	struct object_id **list;
> +	int nr;
> +	int alloc;
> +};

What is the typical access pattern for this data structure?  If it
is pretty much "allocate and grow as we find more", then a dynamic
array of struct (rather than a dynamic array of pointers to struct)
would be a lot more appropriate.  IOW

	struct packed_oid_list {
		struct object_id *list;
		int nr, alloc;
	};

The version in the posted patch has to pay malloc overhead plus an
extra pointer for each object id in the list; unless you often
replace elements in the list randomly and/or you borrow object ID
field in other existing data structure whose lifetime is longer than
this list by pointing at it, I do not see how the extra indirection
is worth it.