HPCC-32791 Partition the index LRU cache to reduce contention

[ghalliday]

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Testing:

[ghalliday]

Pushed for initial review. It needs more cleanup - particularly adding some functions into CNodeMRUCache to remove the iterators from the CNodeCache functions. I will test fully later, and paste some concrete numbers.
Initial numbers from a previous iteration of this branch showed 5-10% improvement for old index format and <5% for new index format. (The latter is possibly because my test is no longer saturating the workers.)

[github-actions]

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-32791

Jirabot Action Result:
Workflow Transition To: Merge Pending
Updated PR

[ghalliday]

I have rebased and rerun tests after sorting out the confusing inconsistent timings (HPCC-32814)
The following timings are min, median for 5 runs:
default, before: 5.688, 5.720
default, after: 5.345 5.362
inplace, before: 3.415 3.434
inplace, after: 2.854 2.921
An improvement of ~5% for default compression and 15% for new inplace compression.

[mckellyln]

Are these backwards ?

[ghalliday]

unlikely() is correct - because the code only reaches this point if there was a match in the cache, but the node associated with that entry has not been loaded yet.
I will add a comment to clarify why.

[mckellyln]

all good.

[mckellyln]

I think this is a great addition.
Just one ques about if alreadyExists is a more typical a likely or unlikely expectation.

[mckellyln]

Approved.