[producer] Add partial update, delete, and batch file mode to ProducerTool

[sixpluszero]

Problem Statement

The ProducerTool CLI currently only supports full-value put and delete-by-null-value operations, one record at a time. This has several limitations:

• No partial update support: Users cannot update individual fields of a record without replacing the entire value. This is especially painful for records with many fields where only one needs to change.
• No explicit delete flag: Deleting a record requires the unintuitive convention of passing -v "null".
• No batch mode: Writing multiple records requires repeated CLI invocations, each incurring connection setup and schema lookup overhead.

Solution

Three new CLI options are added to ProducerTool:

1. Partial update (-u/--update)

Uses VeniceProducer.asyncUpdate() with UpdateBuilder to modify individual fields. Supports:

• Field replacement: {"fieldName": "newValue"} → setNewFieldValue
• List append: {"listField": {"$addToList": [...]}} → setElementsToAddToListField
• List remove: {"listField": {"$removeFromList": [...]}} → setElementsToRemoveFromListField
• Map add: {"mapField": {"$addToMap": {...}}} → setEntriesToAddToMapField
• Map remove: {"mapField": {"$removeFromMap": [...]}} → setKeysToRemoveFromMapField

2. Explicit delete (-d/--delete)

Deletes a record by key without requiring -v. The existing -v "null" convention still works for backward compatibility.

3. Batch file mode (-f/--file)

Reads a JSON Lines file where each line specifies key, value, and optional operation (put/update/delete, default: put). Example:

{"key": "k1", "value": {"name": "Alice"}, "operation": "put"}
{"key": "k2", "value": {"tags": {"$addToList": ["new"]}}, "operation": "update"}
{"key": "k3", "value": "null", "operation": "delete"}

Performance: Schemas are fetched once before processing and cached, avoiding per-record router round-trips. (RouterBasedStoreSchemaFetcher has no internal caching.)

Error handling: Stops on first error, reports how many records succeeded before the failure.

Code changes

• Added new code behind a config. If so list the config names and their default values in the PR description.
  • No new configs. Features are controlled by CLI flags only.
• Introduced new log lines.

Concurrency-Specific Checks

• Code has no race conditions or thread safety issues.
  • All new code runs single-threaded in the CLI main method.
• Proper synchronization mechanisms (e.g., synchronized, RWLock) are used where needed.
  • N/A — single-threaded CLI tool.
• No blocking calls inside critical sections that could lead to deadlocks or performance degradation.
• Verified thread-safe collections are used (e.g., ConcurrentHashMap, CopyOnWriteArrayList).
  • N/A — no shared mutable state.
• Validated proper exception handling in multi-threaded code to avoid silent thread termination.

How was this PR tested?

• New unit tests added.
• New integration tests added.
• Modified or extended existing tests.
• Verified backward compatibility (if applicable).
  • Existing CLI usage (-k + -v for put, -v "null" for delete) works unchanged.
  • All existing unit tests pass.

Does this PR introduce any user-facing or breaking changes?

• No. You can skip the rest of this section.
• Yes. Clearly explain the behavior change and its impact.

New CLI options added (all additive, no breaking changes):

• -u/--update: Perform partial update instead of full put
• -d/--delete: Delete a record by key (no -v needed)
• -f/--file: Batch mode from a JSON Lines file

Minor change: -k and -v are no longer unconditionally required — they are validated contextually (required unless -f or -d is used). This does not break any existing valid invocations.

[Copilot]

Pull request overview

Adds new CLI capabilities to ProducerTool to support partial updates, explicit deletes, and batch ingestion from a JSON Lines file.

Changes:

• Adds --update (-u) to perform partial updates via VeniceProducer.asyncUpdate() and UpdateBuilder.
• Adds --delete (-d) to delete by key without requiring -v "null".
• Adds --file (-f) JSONL batch mode and caches schemas up front to reduce router calls.

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