[PATCH 3 of 5] extdata: add basic caching

[Pierre-Yves David]

On 09/22/2016 08:21 PM, Matt Mackall wrote:
> # HG changeset patch
> # User Matt Mackall <mpm at selenic.com>
> # Date 1474294391 18000
> #      Mon Sep 19 09:13:11 2016 -0500
> # Node ID 133b35066bef5d9c31d13c4f0b2e4a50d1ceae87
> # Parent  9c8847df32a0c5045e60aded2e03a9c97507f909
> extdata: add basic caching
>
> Sources used for log templating will be queried for every changeset
> printed. So we need a cache. We attach the cache to the repo object to
> give it a bounded lifetime.
>
> diff -r 9c8847df32a0 -r 133b35066bef mercurial/scmutil.py
> --- a/mercurial/scmutil.py	Mon Sep 19 09:05:00 2016 -0500
> +++ b/mercurial/scmutil.py	Mon Sep 19 09:13:11 2016 -0500
> @@ -1453,6 +1453,14 @@
>          raise error.Abort(_("extdata doesn't support parameters yet"),
>                            hint=_("use double % for escaping"))
>
> +    # we cache external data sources for the lifetime of a repo object
> +    # users like log templates may consult a data source very frequently
> +    if not util.safehasattr(repo, "_extdatacache"):
> +        repo._extdatacache = {}
> +    cache = repo._extdatacache
> +    if spec in cache:
> +        return cache[spec]
> +

While caching is obviously necessary, repo-life caching is likely to 
provide bogus result with long lived process like chg or the command 
server. We probably needs more aggressive invalidation. What about 
caching the data for each "commands" as a start.

(that cache question is vast, because in some case we probably want to 
have a very strong caching with on disk version, but that is adventure 
for another castle imho)

Cheers,

-- 
Pierre-Yves David