Optimize exact XTRIM MAXLEN zero

[sarthakaggarwal97]

Exact XTRIM key MAXLEN = 0 removes every stream entry while retaining the stream key and its metadata. The generic path removes radix-tree nodes individually and repeatedly re-positions its iterator, even though the final entry tree must be empty.

This change adds a fast path for exact scenario.

Workload	Baseline RPS	Candidate RPS	Change
XTRIM MAXLEN = 0	14,875.81	36,910.15	+148.12%

Found this fast path while debugging with Codex!

[coderabbitai]

📝 Walkthrough

Walkthrough

streamTrim() now fast-paths exact unlimited MAXLEN 0 trimming by replacing the radix tree and resetting metadata. A unit test verifies deletion count, key retention, and empty-stream metadata.

Changes

Stream trimming

Layer / File(s)	Summary
MAXLEN zero fast path src/t_stream.c, tests/unit/type/stream.tcl	Exact unlimited MAXLEN 0 trimming clears all entries, resets stream length and first ID, returns the deleted count, and verifies the stream key and metadata remain present.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: cjx-zar, smkher, murphyjacob4, jsoref, ronen-kalish

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: an exact XTRIM MAXLEN=0 optimization.
Description check	✅ Passed	The description accurately describes the new fast path and its performance impact.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

🧹 Nitpick comments (1)

tests/unit/type/stream.tcl (1)

722-732: 🎯 Functional Correctness | 🔵 Trivial | ⚡ Quick win

Exercise multiple radix-tree nodes.

Two entries do not guarantee multiple nodes, so this test does not prove that the entire tree is cleared. Force a small stream-node-max-entries, add entries across several nodes, then assert XRANGE is empty and radix-tree-keys is zero before restoring the configuration.

Suggested test expansion

     r DEL mystream
-    r XADD mystream 1-0 f v
-    r XADD mystream 2-0 f v
-    assert_equal 2 [r XTRIM mystream MAXLEN = 0]
+    r config set stream-node-max-entries 1
+    for {set j 1} {$j <= 3} {incr j} {
+        r XADD mystream $j-0 f v
+    }
+    assert_equal 3 [r XTRIM mystream MAXLEN = 0]
     assert_equal 1 [r EXISTS mystream]
     set reply [r XINFO STREAM mystream]
     assert_equal 0 [dict get $reply length]
-    assert_equal "2-0" [dict get $reply last-generated-id]
+    assert_equal {} [r XRANGE mystream - +]
+    assert_equal 0 [dict get $reply radix-tree-keys]
+    assert_equal "3-0" [dict get $reply last-generated-id]
     assert_equal "0-0" [dict get $reply recorded-first-entry-id]
+    r config set stream-node-max-entries 100

🤖 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 `@tests/unit/type/stream.tcl` around lines 722 - 732, Update the test XTRIM
with MAXLEN 0 keeps an empty stream key to temporarily set
stream-node-max-entries to a small value, add enough entries to span multiple
radix-tree nodes, and restore the configuration afterward. After trimming,
retain the existing stream metadata assertions and also verify XRANGE returns no
entries and radix-tree-keys is zero.

🤖 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.

Nitpick comments:
In `@tests/unit/type/stream.tcl`:
- Around line 722-732: Update the test XTRIM with MAXLEN 0 keeps an empty stream
key to temporarily set stream-node-max-entries to a small value, add enough
entries to span multiple radix-tree nodes, and restore the configuration
afterward. After trimming, retain the existing stream metadata assertions and
also verify XRANGE returns no entries and radix-tree-keys is zero.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 0313e46e-71fb-4439-8f7e-82236d05c6c8

📥 Commits

Reviewing files that changed from the base of the PR and between cdf98a2 and 9556b2f.

📒 Files selected for processing (2)

• src/t_stream.c
• tests/unit/type/stream.tcl

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.85%. Comparing base (cdf98a2) to head (9556b2f).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #4161      +/-   ##
============================================
+ Coverage     76.82%   76.85%   +0.03%     
============================================
  Files           162      162              
  Lines         81433    81441       +8     
============================================
+ Hits          62561    62594      +33     
+ Misses        18872    18847      -25     

Files with missing lines	Coverage Δ
src/t_stream.c	94.53% <100.00%> (+0.02%)	⬆️

... and 21 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[sarthakaggarwal97]

@enjoy-binbin any concerns do you see? should we merge?