Duy Nguyen <pclo...@gmail.com> writes:

> On Mon, Apr 28, 2014 at 02:18:44PM -0700, Shawn Pearce wrote:
>> > The read penalty is not addressed here, so I still pay 14MB hashing
>> > cost. But that's an easy problem. We could cache the validated index
>> > in a daemon. Whenever git needs to load an index, it pokes the daemon.
>> > The daemon verifies that the on-disk index still has the same
>> > signature, then sends the in-mem index to git. When git updates the
>> > index, it pokes the daemon again to update in-mem index. Next time git
>> > reads the index, it does not have to pay I/O cost any more (actually
>> > it does but the cost is hidden away when you do not have to read it
>> > yet).
>> If we are going this far, maybe it is worthwhile building a mmap()
>> region the daemon exports to the git client that holds the "in memory"
>> format of the index. Clients would mmap this PROT_READ, MAP_PRIVATE
>> and can then quickly access the base file information without doing
>> further validation, or copying the large(ish) data over a pipe.
> The below patch implements such a daemon to cache the index. It takes
> 91ms and 377ms to load a 25MB index with and without the daemon. I use
> share memory instead of pipe, but the format is still "on disk" not
> "in memory" for simplicity. I think we're good even without in memory
> format.

Interesting ;-).
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