feat(transaction): add Transaction::start_ts and scan_unbounded by ariesdevil · Pull Request #554 · tikv/client-rust

ariesdevil · 2026-07-24T14:33:31Z

start_ts exposes the transaction's TSO start timestamp, matching client-go's KVTxn.StartTS.
scan_unbounded (on Transaction and Snapshot) returns all pairs in a range by paginating internally in batches of 1024, matching client-go's KVSnapshot.
Iter semantics: a short page means the range is exhausted, a full page advances past the last key.

Summary by CodeRabbit

New Features
- Added unbounded range scanning for both snapshots and transactions via a new lazy scanner that fetches results in batches until completion.
- Introduced a public scanner API for iterating over key-value pairs.
- Exposed the scanner type as part of the public transaction surface.
Tests
- Added/updated tests for the transaction start timestamp.
- Added coverage for unbounded scan pagination, validating batch size, ordering, and returned values.

ti-chi-bot · 2026-07-24T14:33:36Z

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ti-chi-bot · 2026-07-24T14:33:42Z

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coderabbitai · 2026-07-24T14:34:02Z

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Reviewing files that changed from the base of the PR and between f2bd080 and 69be17a.

📒 Files selected for processing (4)

src/lib.rs
src/transaction/mod.rs
src/transaction/snapshot.rs
src/transaction/transaction.rs

🚧 Files skipped from review as they are similar to previous changes (3)

src/lib.rs
src/transaction/mod.rs
src/transaction/snapshot.rs

📝 Walkthrough

Walkthrough

Transaction adds lazy, paginated unbounded range scanning through a public Scanner. Snapshot delegates the API, Scanner is re-exported publicly, and tests validate pagination and transaction timestamp behavior.

Changes

Transaction scanning

Layer / File(s)	Summary
Transaction scan implementation `src/transaction/transaction.rs`	Adds lazy scanner construction and 256-item pagination using buffered results, successor keys, and short-page EOF detection.
Snapshot and public API surface `src/transaction/snapshot.rs`, `src/transaction/mod.rs`, `src/lib.rs`	Adds Snapshot delegation and re-exports `Scanner` from the transaction module and crate root.
Scanner and timestamp validation `src/transaction/transaction.rs`	Tests timestamp access, scan limits, pagination calls, ordering, and returned values.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Snapshot
  participant Transaction
  participant PdClient
  Snapshot->>Transaction: scan_unbounded(range)
  Transaction->>PdClient: scan(start, end, batch size)
  PdClient-->>Transaction: page of KvPair results
  Transaction->>PdClient: scan(next key, end, batch size)
  PdClient-->>Transaction: final page of KvPair results
  Transaction-->>Snapshot: KvPair results

Suggested reviewers: eduralph, iosmanthus

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding transaction start timestamp access and unbounded scan support.
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.

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Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@src/transaction/transaction.rs`:
- Around line 122-127: Update the documentation for the transaction start
timestamp accessor to describe start_ts solely as the transaction’s read
timestamp. Remove claims that writes become visible at this timestamp or that
its physical component is suitable for commit, lease, or fencing semantics;
clarify that visibility is determined by the commit timestamp.

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src/transaction/snapshot.rs
src/transaction/transaction.rs

you06

rest LGTM

you06 · 2026-07-28T15:12:52Z

+            if let Some(last) = page.last() {
+                start = last.key().clone().next_key();
+            }
+            out.extend(page);


We can't estimate the data size in a range, so buffer them in memory is danger to me, it can easily cause OOM in the client side.

Fixed, aligned to the client-go's behavior, PTAL again.

coderabbitai

Actionable comments posted: 2

🤖 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.

Inline comments:
In `@src/transaction/transaction.rs`:
- Around line 122-134: Consolidate the duplicate accessors by making either
start_ts or the existing start_timestamp delegate to the other, with both
preserving the current timestamp value and public API behavior. Prefer retaining
the established accessor unless the project’s compatibility policy explicitly
phases it out, and avoid maintaining two independent implementations.
- Around line 1246-1248: Reconcile SCAN_UNBOUNDED_BATCH_SIZE with the documented
scan batch size: choose the intended value (256 or 1024), update the constant or
its description accordingly, and replace the inaccurate client-go
DefaultScanBatchSize reference with a valid upstream source or remove the
attribution.

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📥 Commits

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📒 Files selected for processing (4)

src/lib.rs
src/transaction/mod.rs
src/transaction/snapshot.rs
src/transaction/transaction.rs

🚧 Files skipped from review as they are similar to previous changes (1)

src/transaction/snapshot.rs

Signed-off-by: Yijun Zhao <ariesdevil77@gmail.com>

ti-chi-bot Bot added contribution This PR is from a community contributor. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. dco-signoff: no Indicates the PR's author has not signed dco. labels Jul 24, 2026

ti-chi-bot Bot added the first-time-contributor Indicates that the PR was contributed by an external member and is a first-time contributor. label Jul 24, 2026

ariesdevil force-pushed the dev_ariesdevil branch from da909e8 to dd640ed Compare July 24, 2026 14:35

ti-chi-bot Bot added dco-signoff: yes Indicates the PR's author has signed the dco. and removed dco-signoff: no Indicates the PR's author has not signed dco. labels Jul 24, 2026

coderabbitai Bot reviewed Jul 24, 2026

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Comment thread src/transaction/transaction.rs Outdated

ariesdevil force-pushed the dev_ariesdevil branch 3 times, most recently from 2bfa214 to 297da6c Compare July 27, 2026 09:36

you06 reviewed Jul 28, 2026

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ariesdevil force-pushed the dev_ariesdevil branch from 297da6c to f2bd080 Compare July 28, 2026 15:36

coderabbitai Bot reviewed Jul 28, 2026

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Comment thread src/transaction/transaction.rs Outdated

Comment thread src/transaction/transaction.rs

feat(transaction): add Transaction::start_ts and scan_unbounded

69be17a

Signed-off-by: Yijun Zhao <ariesdevil77@gmail.com>

ariesdevil force-pushed the dev_ariesdevil branch from f2bd080 to 69be17a Compare July 28, 2026 16:00

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feat(transaction): add Transaction::start_ts and scan_unbounded - #554

feat(transaction): add Transaction::start_ts and scan_unbounded#554
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