Improve document index

[ChristianGruen]

Replacing documents with REPLACE or db:replace takes some time and could possibly be sped up by a better persistent document index.

[ChristianGruen]

Related to #798, #568, #429.

[cfoster]

Thanks for taking a look at this Christian. If you manage to speed up the replacement of fragments, could the ADD and STORE commands make use of this? Or, at least something where a client is trying to insert a fragment doesn't need to know whether the URI is currently in use or not.

[ChristianGruen]

I’m not sure why you think ADD could benefit from this speedup, because ADD is faster anyway, because it ignores duplicate paths. Could you please give me more info on what you mean?

Btw, STORE is different, as it simply stores files in the directory structure. This way, existing files will automatically be overwritten, but if an XML file exists with the same resource path, it won’t be replaced (well, this rarely happens).

[cfoster]

Still aware of this and will come back.

[ChristianGruen]

I believe this issue is more or less finalized. @cfoster and others: Feedback is welcome!