[Tiered Cache] Using a single cache manager for all ehcache disk caches

[sgup432]

Description

Earlier while trying to create N ehcache disk caches, we were creating those via N cache managers which had their own disk write thread pools (so total N). We create N disk caches based on tiered cache setting and it is decided based on number of CPU cores. So essentially we were creating (CPU_CORE * 4) disk write threads which is a lot and can cause CPU spikes with tiered cache enabled.

This change essentially creates a single cache manager, and all subsequent caches are created via this single manager. Through this we only have one disk write thread pool and is configured to have between 2 and CPU * 1.5 threads.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• [ ] Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 69bbc69: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 112a96b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for cc0fea8:

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for fafae93: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 85.84906% with 15 lines in your changes missing coverage. Please review.

Project coverage is 72.41%. Comparing base (2d42bd0) to head (13b2e85).
Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
...arch/cache/store/disk/EhcacheDiskCacheManager.java	82.66%	10 Missing and 3 partials ⚠️
.../opensearch/cache/store/disk/EhcacheDiskCache.java	92.30%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17513      +/-   ##
============================================
+ Coverage     72.39%   72.41%   +0.01%     
- Complexity    66066    66235     +169     
============================================
  Files          5358     5385      +27     
  Lines        306500   307200     +700     
  Branches      44409    44560     +151     
============================================
+ Hits         221888   222447     +559     
- Misses        66474    66543      +69     
- Partials      18138    18210      +72     

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[github-actions]

❕ Gradle check result for 13b2e85: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-17513-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 58eb44e7ece913aca6de34d32f6b837a512541ae
# Push it to GitHub
git push --set-upstream origin backport/backport-17513-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-17513-to-2.x.