Re: [GSOC][QUESTION] How to parse the properties of the object at once

[Junio C Hamano <gitster@pobox.com>]

ZheNing Hu <adlternative@gmail.com> writes:

> This means that I shouldn't touch the content of struct commit. So I see the
> code of `commit-slab`, it seems that it is doing additional parsing.

We should keep what is in "struct commit" and parsing overhead to
the minimum, as it matters to performance (especially when auxiliary
data structures like commit-graph are not available for the part of
history).  If some pieces of data (like "from this byte to the end
is %(body)") do not matter in commit traversal, they are optional,
and (1) we should not always parse them out, instead we should do so
only on demand, and (2) we should not add members for them in the
commit object, but use commit slabs to store them.

As to the slab, it is not like you have to have a slab per these
optional fields you may want to parse.  If for example you need the
authorship ident and timestamp, even if you do not need committer
ident and timestamp, it is plausible to have a type of slab that
holds these four data items together (and only fill parts of them
that are actually requested by the callers).  Also, things that are
strings may want to be stored as a relative offset into the commit
buffer, instead of duplicated copies of string values.