Add support to dynamically resize threadpools size

[gbbafna]

Description

Adds capability to change thread pool sizes for all threadpools defined in core

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 71df521: FAILURE

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[github-actions]

❌ Gradle check result for 8d75efd: FAILURE

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[jed326]

Thanks @gbbafna! I like the idea of dynamically tuning the threadpool size but I am worried there are some sharp edges for users with a cluster setting.

Today the threadpool size can be set per-node via the opensearch.yml, so in cases where there is a mix of hardware type across the cluster each node can have it's own configuration. This is pretty typical for the cluster manager nodes and the data nodes to be of different instance types, so the concern is that we could accidentally adversely affect one instance type by setting the cluster wide setting.

For example, if we increase the snapshots threadpool size across the cluster, that might improve the performance of taking a snapshot on the data nodes, but have adverse effects on cloning a snapshot on the cluster manager nodes.

[dbwiddis]

Overall, I love the idea to tune the threadpool size. This will give end users the option to get the best out of their opensearch cluster.

I love the idea of tuning, but that also just adds a lot more complexity that barely any of us understand! What should it be?

Giving one threat pool more resources should ideally be balanced by a reduction in another, but how do we know? Is there any way to have an overall "max threads across all these different pools" constraint to let people tweak up one pool as long as they constrain others? Are there stats that let us measure how many times a pool is maximized?

[gbbafna]

Thanks @gbbafna! I like the idea of dynamically tuning the threadpool size but I am worried there are some sharp edges for users with a cluster setting.

Today the threadpool size can be set per-node via the opensearch.yml, so in cases where there is a mix of hardware type across the cluster each node can have it's own configuration. This is pretty typical for the cluster manager nodes and the data nodes to be of different instance types, so the concern is that we could accidentally adversely affect one instance type by setting the cluster wide setting.

For example, if we increase the snapshots threadpool size across the cluster, that might improve the performance of taking a snapshot on the data nodes, but have adverse effects on cloning a snapshot on the cluster manager nodes.

This are quite valid points @jed326, thanks for them . Definitely, there are sharp edges with this feature. We would recommend only expert users to tune this up . Also since its dynamic, users can easily revert it as well on observation of degradation. On a higher level , i would say we should have a different thread pool for cloning and create snapshot . Recently we introduced another threadpool for deletion as well to independently scale up and down.

Also i would put in the documentation to not use this if you have a heterogeneous cluster . Practically , I have seen most of the clusters as homogeneous only .

[gbbafna]

Overall, I love the idea to tune the threadpool size. This will give end users the option to get the best out of their opensearch cluster.

I love the idea of tuning, but that also just adds a lot more complexity that barely any of us understand! What should it be?

Giving one threat pool more resources should ideally be balanced by a reduction in another, but how do we know?

Thanks @dbwiddis . I agree it is tricky to tune it and would document that only experts should tune it on a need basis and monitor for any degradation.

how do we know? - There would be some experimentation required to figure out what is best for a given configuration.

Is there any way to have an overall "max threads across all these different pools" constraint to let people tweak up one pool as long as they constrain others?

We can think about this if this will benefit our users .

Are there stats that let us measure how many times a pool is maximized?

Yes, we have thread pool stats to figure that out .

[github-actions]

❌ Gradle check result for 4bedb9c: FAILURE

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[github-actions]

❌ Gradle check result for b161100: FAILURE

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[github-actions]

❌ Gradle check result for cc11f7e: FAILURE

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[ashking94]

LGTM overall, have left some comments.

[github-actions]

❕ Gradle check result for 2df2683: 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.

[codecov]

Codecov Report

Attention: Patch coverage is 53.44828% with 27 lines in your changes missing coverage. Please review.

Project coverage is 72.00%. Comparing base (691f725) to head (2df2683).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
...ain/java/org/opensearch/threadpool/ThreadPool.java	52.63%	25 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16236      +/-   ##
============================================
- Coverage     72.06%   72.00%   -0.06%     
+ Complexity    64822    64786      -36     
============================================
  Files          5308     5308              
  Lines        302574   302613      +39     
  Branches      43710    43723      +13     
============================================
- Hits         218048   217897     -151     
- Misses        66648    66797     +149     
- Partials      17878    17919      +41     

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[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-16236-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 35c366ddc794e0600184cf406c06ae65061e28ce
# Push it to GitHub
git push --set-upstream origin backport/backport-16236-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-16236-to-2.x.