hemanth-19 opened a new pull request, #4600:
URL: https://github.com/apache/cassandra/pull/4600
## Summary
- Adds `nodetool tpstatsjson` — a new read-only subcommand that prints
thread-pool and dropped-message statistics as a single, deterministic
JSON object to stdout.
- Output is **pretty-printed** (two-space indent, one value per line).
This is deliberate: when a single counter ticks from `5` to `6` the
diff is one line. Compact single-line JSON would collapse the entire
document into one line, turning every change into a full-document
replacement and making diffs uninformative. Users who need compact
output for transport can pipe through `jq -c`.
- Keys are alphabetically sorted at every nesting level (via Jackson
`ORDER_MAP_ENTRIES_BY_KEYS`), making the output safe to `diff` in CI
without post-processing.
- Two-tier error handling: section-level and per-metric failures are
each caught independently and recorded in a top-level `errors` object
(present only when a failure actually occurs). The `"N/A"` sentinel
from unregistered MBeans is normalised to JSON `null` — data
normalisation, not an error.
## Why a new command instead of fixing `tpstats -F json`
`tpstats -F json` already emits JSON, but its key ordering is
non-deterministic: the data flows through `TpStatsHolder.convert2Map()`
and `StatsPrinter.JsonPrinter`, both of which use plain `HashMap`.
Switching those to sorted maps would silently change the output that
existing scripts and CI pipelines already consume and may parse or diff
in an order-dependent way. A dedicated command with its own
`ObjectWriter` isolates the sorted-keys contract entirely — no existing
code path is touched, no operator is surprised.
## Files changed
| File | What |
|------|------|
| `src/java/.../TpStatsJson.java` | Command implementation (198 lines) |
| `src/java/.../NodetoolCommand.java` | One-line registration in subcommands
array |
| `test/resources/nodetool/help/tpstatsjson` | Golden help file for
`NodetoolHelpCommandsOutputTest` |
| `test/unit/.../TpStatsJsonTest.java` | Six tests: validity, structure, key
ordering, live-data visibility, N/A normalisation, errors serialisation |
## Static verification notes
All API call sites and data contracts were cross-checked against the
existing codebase before submission:
- **NodeProbe signatures:** `getThreadPools()` returns
`Multimap<String,String>` (`NodeProbe:2062`);
`getThreadPoolMetric(path, pool, metric)` returns `Object`
(`NodeProbe:1955`); `getDroppedMessages()` returns
`Map<String,Integer>` (`NodeProbe:1672`). Every call site in
`TpStatsJson.execute()` matches these signatures exactly.
- **Metric name parity with TpStatsHolder:** The five JMX attribute
names used — `ActiveTasks`, `PendingTasks`, `CompletedTasks`,
`CurrentlyBlockedTasks`, `TotalBlockedTasks` — are the identical set
fetched by `TpStatsHolder:46–50`. No new MBean attributes are
introduced.
- **Iteration pattern:** The
`for (Map.Entry<String,String> tp : probe.getThreadPools().entries())`
loop is the established pattern at `TpStatsHolder:43`.
- **Output path:** `probe.output().out.println(…)` is the canonical
write mechanism, used by 70+ existing commands. `Output.out` is
`public final PrintStream` (`Output:27`).
- **Golden help file wrapping:** The NAME-section line break was
verified by computing PicoCLI's 80-column word-wrap and
cross-checking against the `failuredetector` reference file (a
command with no custom options, structurally identical). SYNOPSIS
and OPTIONS sections are the shared global-JMX-option boilerplate.
If the file is off by even one character `NodetoolHelpCommandsOutputTest`
will surface the exact diff; regenerate via `NodetoolHelpGenerator`.
## Test plan
Tests could not be executed locally (no `ant` / JDK runtime in the
development environment). The following three CI targets must pass:
- [ ] `ant testsome
-Dtest.name=org.apache.cassandra.tools.nodetool.TpStatsJsonTest`
— all six new tests
- [ ] `ant testsome
-Dtest.name=org.apache.cassandra.tools.nodetool.TpStatsTest`
— regression: existing tpstats behaviour unchanged
- [ ] `ant testsome
-Dtest.name=org.apache.cassandra.tools.nodetool.NodetoolHelpCommandsOutputTest`
— golden help file validation (parameterised; auto-discovers
tpstatsjson)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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