Storages: Enhance storage logging details

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #10950

Problem Summary:

When diagnosing TiFlash storage and query issues in production, existing logs and execution summaries lack enough context to distinguish scan types and understand slow storage operations:

• TableScan execution summary JSON does not indicate whether the scan is a regular TableScan or PartitionTableScan.
• Split-based ingest logs are mostly at DEBUG level and do not include elapsed time, making slow ingest hard to spot.
• Segment split/merge-delta finish logs do not include the trigger reason.
• Segment info strings miss stable column count and on-disk DMFile size.
• FileCache download success logs do not distinguish foreground vs background downloads.
• gtest_kvstore_fast_add_peer is flaky in CI and FAP is not planned for short-term support.

What is changed and how it works?

Add observability improvements for TableScan statistics and storage layer logging.

- Expose `is_partition_table_scan` in TableScan execution summary JSON.
- Add elapsed-time logging for split ingest; promote slow paths (>10s) from DEBUG to INFO.
- Log split/merge-delta reason in segment operation finish logs.
- Enrich Segment::info() with stable column count and DMFile on-disk bytes.
- Log FileCache download type (Foreground/Background) on successful download.
- Disable flaky gtest_kvstore_fast_add_peer test.

TableScan statistics

• Cache is_partition_table_scan in TableScanStatistics constructor via executor->has_partition_table_scan().
• Output "is_partition_table_scan": true/false in appendExtraJson, so execution summary / slow query analysis can tell partition scans apart.

DeltaMerge storage logging

• Introduce SplitIngestLogContext in ingestDTFilesUsingSplit:
  • Track elapsed time across split ingest phases.
  • Use LOG_IMPL to emit begin/finish logs at INFO when elapsed > 10s, otherwise DEBUG.
  • Add elapsed_seconds to per-file ingest attempt logs (INFO).
• Log reason in segmentSplit and segmentMergeDelta finish logs via magic_enum::enum_name(reason).
• Extend Segment::info() with stable_cols and dmf_disk_bytes.
• Add DMFile::getNumColumns() and StableValueSpace::getDMFilesNumColumns().

S3 FileCache

• Add FileCache::DownloadType (Foreground / Background).
• Include download type in downloadImpl success log for easier disagg read path analysis.

Tests

• Wrap gtest_kvstore_fast_add_peer.cpp with #if 0 and document why (flaky CI, FAP not planned for short-term support).

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

Summary by CodeRabbit

• New Features
  • Enhanced table-scan status details with partition-scan indicator and added stable scan summary fields.
  • Added column-count reporting to segment/stable summaries.
  • S3 file-download logging now distinguishes foreground vs background transfers.
• Bug Fixes
  • Improved split-ingest and completion logging with elapsed time and “reason” context for easier troubleshooting.
  • Disabled a flaky KV store test from building/running.
• Refactor
  • Clarified the split-vs-column-file ingest branching for improved readability.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 1e4b17ca-f1e0-49aa-a981-8c35a872b0ca

📥 Commits

Reviewing files that changed from the base of the PR and between f6104ca and 627efec.

📒 Files selected for processing (5)

• tests/docker/next-gen-columnar-yaml/cluster.yaml
• tests/docker/next-gen-utils/Makefile
• tests/docker/next-gen-yaml/cluster.yaml
• tests/fullstack-test-next-gen-columnar/_env.sh
• tests/fullstack-test-next-gen/_env.sh

✅ Files skipped from review due to trivial changes (1)

• tests/docker/next-gen-columnar-yaml/cluster.yaml

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📝 Walkthrough

Walkthrough

This PR adds partition-table-scan metadata and richer DeltaMerge/FileCache logging, disables one flaky KVStore test, and renames several next-gen test image and branch defaults from -next-gen to -nextgen.

Changes

Logging and diagnostics enhancements

Layer / File(s)	Summary
Partition table scan flag in statistics dbms/src/Flash/Statistics/TableScanImpl.h, dbms/src/Flash/Statistics/TableScanImpl.cpp	Adds is_partition_table_scan to table-scan statistics, initializes it from executor metadata, and includes it in the JSON payload.
Timing-aware split ingest logging dbms/src/Storages/DeltaMerge/DeltaMergeStore_Ingest.cpp	Adds a stopwatch-backed log context for split ingest, emits elapsed seconds in begin/per-file/finish logs, and rewrites the split-replace branch calls.
Segment split and merge reasons dbms/src/Storages/DeltaMerge/DeltaMergeStore_InternalSegment.cpp	Adds reason to segment split and merge-delta completion logs and keeps nearby comments updated.
Stable file column counts in segment info dbms/src/Storages/DeltaMerge/File/DMFile.h, dbms/src/Storages/DeltaMerge/StableValueSpace.{h,cpp}, dbms/src/Storages/DeltaMerge/Segment.cpp	Adds column-count accessors and extends Segment::info() with stable column and byte fields.
FileCache download type tracking dbms/src/Storages/S3/FileCache.{h,cpp}	Adds a download-type enum, threads it through downloadImpl, logs it on success, and updates foreground/background call sites.
Disable flaky KVStore fast add peer test dbms/src/Storages/KVStore/tests/gtest_kvstore_fast_add_peer.cpp	Disables the test file from compilation with a #if 0 guard.

Next-gen test image and branch tag updates

Layer / File(s)	Summary
Docker image tag defaults tests/docker/next-gen-utils/Makefile, tests/docker/next-gen-yaml/cluster.yaml, tests/docker/next-gen-columnar-yaml/cluster.yaml	Updates PD, TiKV, TiDB, TiFlash, and worker image tags from -next-gen to -nextgen.
Fullstack branch defaults tests/fullstack-test-next-gen/_env.sh, tests/fullstack-test-next-gen-columnar/_env.sh	Updates exported branch defaults and normalization rules to use *-nextgen and cloud-engine-nextgen names.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• pingcap/tiflash#10905: Also changes TableScanStatistics::appendExtraJson in dbms/src/Flash/Statistics/TableScanImpl.cpp.
• Suggested reviewers: yongman, CalvinNeo

Poem

A rabbit hopped through logs and tags,
With branch names new and fewer flags.
It sniffed the scans, then bounded high,
While split ingest ticked by with a sigh.
Hop, hop — the build burrow shines tonight 🐇

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR includes many unrelated changes beyond #10950, such as split-ingest timing logs, FileCache logging, and test/image tag updates.	Split unrelated storage logging, test, and Docker image updates into separate PRs, leaving only the partition-table-scan logging change here.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is related to the storage/logging changes, though it is broader than the main partition-scan observability update.
Description check	✅ Passed	The PR description matches the template and includes the issue, problem summary, change summary, checklist, and release note.
Linked Issues check	✅ Passed	The TableScan JSON adds is_partition_table_scan, which addresses #10950 by distinguishing partition table scans in logging output.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[JaySon-Huang]

/retest