feat(config): prefer read concurrency limit

[yordis]

• Operators need one clear read concurrency knob that describes the runtime pressure being controlled.
• Conflicting old and new read concurrency settings should fail early instead of producing ambiguous startup behavior.

[cursor]

PR Summary

Medium Risk
Renames a database configuration knob used to size read processing, which may break existing deployments still using ReaderThreadsCount/--reader-threads-count and change default behavior (now 0 for autoconfig). Changes are localized but affect startup configuration and runtime read concurrency sizing.

Overview
Updates the server to use a single read-concurrency configuration knob by replacing ReaderThreadsCount with ReadConcurrencyLimit throughout configuration (ClusterVNodeOptions.DatabaseOptions) and startup sizing (ClusterVNode calling ThreadCountCalculator).

Refreshes docs and CLI/YAML/env var names to match (--read-concurrency-limit, ReadConcurrencyLimit, EVENTSTORE_READ_CONCURRENCY_LIMIT) and documents the default as 0 (autoconfig), with log messages updated accordingly.

^{Reviewed by Cursor Bugbot for commit 763b7b2. Bugbot is set up for automated code reviews on this repo. Configure here.}

[coderabbitai]

Walkthrough

This PR renames the read-threading configuration option from ReaderThreadsCount to ReadConcurrencyLimit throughout the codebase. The default value changes from 4 to 0. The change flows through the configuration schema, runtime initialization, user-facing documentation, and internal logging.

Changes

Read Concurrency Configuration Rename

Layer / File(s)	Summary
Configuration schema definition src/EventStore.Core/Configuration/ClusterVNodeOptions.cs	DatabaseOptions property is renamed from ReaderThreadsCount to ReadConcurrencyLimit with default 0.
Configuration consumption in runtime src/EventStore.Core/ClusterVNode.cs	ClusterVNode constructor passes options.Database.ReadConcurrencyLimit instead of ReaderThreadsCount to thread count calculation.
Documentation updates docs/configuration.md, docs/db-config.md, docs/server-settings.md	Configuration tables and sections updated with new flag names (--read-concurrency-limit), YAML keys (ReadConcurrencyLimit), environment variables (EVENTSTORE_READ_CONCURRENCY_LIMIT), and default value 0 across all three documentation files.
Logging message updates src/EventStore.Core/Settings/ThreadCountCalculator.cs	Serilog message templates updated to reference ReadConcurrencyLimit terminology in all thread count calculation paths (configured count, containerized environment, processor-clamped paths).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A reader's name doth change with grace,
From threads counted to limits placed,
Through docs and logs the rename flows,
With zero now as default shows,
This little hop completes the way!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat(config): prefer read concurrency limit' accurately summarizes the main change: replacing ReaderThreadsCount with ReadConcurrencyLimit across configuration files and code.
Description check	✅ Passed	The description explains the rationale for the change: providing a single clear configuration option for read concurrency and enforcing early validation for conflicting settings.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch yordis/feat-read-concurrency-limit

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

docs/configuration.md (1)

202-203: ⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Update stale option name in WhatIf sample.

Line 202 still shows READER THREADS COUNT, which conflicts with the renamed ReadConcurrencyLimit docs on this page.

Suggested doc fix

-         READER THREADS COUNT:                    0 (<DEFAULT>)
+         READ CONCURRENCY LIMIT:                  0 (<DEFAULT>)

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@docs/configuration.md` around lines 202 - 203, Update the stale option name
in the WhatIf sample by replacing the old "READER THREADS COUNT" entry with the
new option name "ReadConcurrencyLimit" so the sample matches the renamed
configuration documented elsewhere; ensure the value and default comment remain
the same (e.g., "ReadConcurrencyLimit: 0 (<DEFAULT>)") and update any nearby
references in the same sample that mention READER THREADS COUNT.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@docs/configuration.md`:
- Around line 202-203: Update the stale option name in the WhatIf sample by
replacing the old "READER THREADS COUNT" entry with the new option name
"ReadConcurrencyLimit" so the sample matches the renamed configuration
documented elsewhere; ensure the value and default comment remain the same
(e.g., "ReadConcurrencyLimit: 0 (<DEFAULT>)") and update any nearby references
in the same sample that mention READER THREADS COUNT.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 73e09c7f-d044-4a63-9057-1ca608ceca49

📥 Commits

Reviewing files that changed from the base of the PR and between 4b0b9f7 and 763b7b2.

📒 Files selected for processing (7)

• docs/configuration.md
• docs/db-config.md
• docs/server-settings.md
• src/EventStore.Core/ClusterVNode.cs
• src/EventStore.Core/Configuration/ClusterVNodeOptions.cs
• src/EventStore.Core/Configuration/ClusterVNodeOptionsValidator.cs
• src/EventStore.Core/Settings/ThreadCountCalculator.cs