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docs(designs): propose ADR-068 bounded retention for the PostgreSQL changelog - #2234
Refs #2170. This proposes ADR-068 for maintainers to decide. It does not implement it.
With the PostgreSQL datastore, nothing deletes from datastore_changelog, so it grows without limit. The report in #2170 shows 42M rows and 90 GB on a ~350-node cluster. The cleanup_changelog() function in docs/postgresql-schema.sql is never called, and the components do not create it.
AGENTS.md asks for an ADR before deleting event-store history on a timer, so this PR proposes the design first. The main points:
Deleting by processed is not safe.MarkProcessed marks an id prefix for the whole table, for all consumers. So cleanup_changelog() and the workaround in the issue can delete rows another consumer has not read.
The bound is the oldest consumer position, as a (changed_at, id) pair, plus the retention, checked on every deleted row. An id alone is not a position, because the poll orders by (changed_at, id) and ids follow allocation order, not time.
Every saved position counts, also a stale one. A token that has not changed for a long time raises an alert, but it is never ignored, because an old last_updated does not prove that a consumer is gone.
The cleaner runs in-process through both store and client-factory connections, including platform-connectors-only deployments, one run at a time under its own advisory lock. Each connection owner cancels and waits for its cleaner before closing its pool. Factory connections do not perform schema setup or DDL. It deletes in batches through an index range scan on idx_changelog_resume_all from fix(store-client): add a changelog index the PostgreSQL change stream poll can use #2233. It is off by default, with new keys, variables and metrics only.
The revised proposal selects a previous-snapshot guard: each run records pg_snapshot_xmin(pg_current_snapshot()) and only uses a horizon observed at least one cleanup interval earlier. A new optional changelog_cleanup_state table shares the full horizon and observation time across owners. The first run seeds it without deleting. Comparisons account for 32-bit row xmin versus xid8; the bounded candidate query checks current row versions after validating the horizon window. No commit-timestamp server setting or older-writer change is required.
The revision also includes acknowledgment-safe idle checkpoints for healthy quiet consumers, with unchanged consumer interfaces and resume-token fields. Idle advancement now requires a fresh activity inspection with no other open or prepared transactions and no hidden activity, followed by a new read snapshot. Its actual candidate pair must precede the inspection fence, and all handed-out deliveries must be acknowledged. Missing visibility or uncertain timestamp ordering defers idle progress; busy databases can conservatively hold cleanup back. Reader rollout is an explicit prerequisite before enabling cleanup; older readers cannot be identified automatically from the unchanged token format.
Invalid retention or cleanup settings warn and disable only the cleaner, without failing startup or ingestion. Seven days is 168h; Go does not accept 7d.
Alternatives considered: a Helm CronJob, calling cleanup_changelog(), deleting in MarkProcessed, ignoring stale tokens, and partitioning. The open questions for maintainers are in the Notes section: the default, and how to recover from a removed component's token.
Earlier measurements checked the candidate age-and-position query on PostgreSQL 16 with a 5M-row changelog and idx_changelog_resume_all. These measurements exclude the selected long-transaction guard; they do not validate a complete cleaner:
With work to do, the batch query is an index range scan with all three conditions in the index condition, and a 10,000-row batch takes 68 ms.
With nothing to delete, it takes 0.12 ms (8 buffers).
When the oldest consumer is behind every old row, it reads 4 buffers.
In a small table with a token at (10:00, id 200), the pair bound keeps a row at (10:05, id 150) and a young row with id 120. A bound on id alone would delete both.
The negative-age review follow-up requires a new short repeatable-read transaction per delete batch, an assigned anchoring xid and the existing validated previous horizon. The guard permits snapshot-visible negative-age versions as well as versions strictly older than the horizon. This prevents a very old frozen prefix from permanently blocking cleanup. Both branches remain behind the retention and consumer-position conditions. Concurrent changes causing serialization failure roll back the entire batch; metrics count committed deletes only. Read committed is not permitted for this predicate.
Type of Change
🐛 Bug fix
✨ New feature
💥 Breaking change
📚 Documentation
🔧 Refactoring
🔨 Build/CI
Component(s) Affected
Health Monitor
Core Service
Fault Management
Janitor
Deployment/Config
API/Interface
Preflight
Plugins
Documentation/CI
New Component
Multiple Components
Other
Testing
Tests pass locally
Manual testing completed
No breaking changes (or documented)
Final branch sync e2f09ad2 includes main 152425f3 without changing the ADR, protocol or index content. Relative to main this PR still changes only three documentation files. Local links, document lengths and whitespace checks pass. The required full gate on the synced revision again passed protobuf, license, module, Renovate, dead-code and unused-code checks, then stopped at the same four Linux boot-ID tests on macOS (339 tests, four failures). Full local validation remains incomplete; this sync does not claim a new runtime or E2E result.
Latest revision 6e1681b6 addresses the negative-age concern. On PostgreSQL 16, explicit synthetic old raw-XID cases cover signed-age boundaries and bounded progress through a modeled negative-age prefix. Separate real-row MVCC tests preserve late root/subtransaction/prepared commits and processed updates, exclude a post-snapshot negative-age insert under repeatable read, demonstrate why read committed is unsafe, and verify 40001 rolls back earlier deletes in the same batch. The prefix fixture uses a separate xid column, not physical ancient tuple headers. A live old-tuple/full-wrap acceptance test remains outstanding before release.
An offline counter-advance fixture failed setup and was abandoned after automatic approval review rejected another retry under the repository retry limit. It is not counted as passing evidence. The ordinary MVCC container was disposed of.
Documentation links, structure, whitespace and lengths pass (ADR 2,993 words, protocol 1,483). make lint-test-all ran on 6e1681b6: protobuf, license, module, Renovate, dead-code and unused-code checks passed, then the same four Linux boot-ID tests failed on macOS (339 tests, four failures). No assertions were weakened; full local validation is not green. No runtime cleaner or new E2E pass is claimed.
Earlier documentation revision 82ae888a addresses the late-commit idle-checkpoint finding. A fresh, network-isolated PostgreSQL 16 prototype reproduced the unsafe saved-tail loss, then passed the proposed conservative fence checks for xid-less/read-only writers, prepared transactions, activity-to-prepare transitions, disabled tracking, hidden visibility and a late no-listener commit returned by subsequent polling. This is SQL-prototype evidence; provider acknowledgment bookkeeping, arbitrary database clock-regression handling and full concurrency/restart release tests remain implementation prerequisites. The new protocol explicitly requires timestamp ordering and defers progress when it cannot be established.
Final ADR/protocol links, structure, whitespace and lengths pass (2,985 / 1,326 words). Ran make lint-test-all on 82ae888a with the corrected isolated tools: protobuf, license, module, Renovate, dead-code and unused-code checks passed; the same four Linux boot-ID syslog tests failed on macOS (339 tests, four failures). No assertions were weakened. The complete local gate is not green. No runtime code or E2E result is claimed by this revision.
Merge follow-up 71ce3faf brings the branch up to main 6ebbc1bd. The only conflict was the ADR index; both ADR-066 and ADR-068 entries are preserved. The proposal and protocol content are unchanged. Local links, ADR structure, document length, index entries and whitespace checks passed. After correcting the isolated Python tool environment to the current protobuf pin, make lint-test-all passed protobuf, license, module, Renovate, dead-code and unused-code checks, then stopped at the same four Linux boot-ID tests on macOS (339 syslog tests, four failures). No assertions were weakened. Full local validation remains incomplete; E2E was not rerun for this index-only conflict resolution.
This is a proposed design, not a cleaner implementation. Validation for 0556cc2a:
ADR structure, local links, whitespace, and document length passed. ADR: 2,986 words; supporting protocol: 1,028 words.
PostgreSQL 16 prototype passed guard warm-up, too-early runs, owner replacement, late top-level/subtransaction/prepared commits, processed updates and VACUUM FREEZE. A later horizon made previously protected rows eligible. Observation times were advanced to model elapsed cleanup intervals.
PostgreSQL relative-age checks passed representative low-ID rollover/equality cases and rejected a full-epoch alias. These are not a live-cluster transaction-counter wrap test; release acceptance still requires wraparound coverage.
A protected prefix produced no deletion, and the actual materialized-candidate plan returned at most 100 candidates. This checks bounded prototype work, not final million-row guarded-query performance.
A repeatable-read empty proof and captured tail left a concurrently committed matching event beyond the saved boundary. Provider in-flight/acknowledgment bookkeeping is specified and remains a future implementation acceptance test.
Nine Go duration/parser enablement cases passed: unset, 0, negative, below-minimum, 24h, 168h, 7d, malformed and overflowing. Startup/ingestion behavior is an acceptance requirement, not implemented code tested by this documentation PR.
Ran make lint-test-all once in the clean isolated revision checkout. Protobuf, license, module, Renovate, dead-code and unused-code gates passed; it stopped at four syslog tests requiring Linux /proc/sys/kernel/random/boot_id, absent on macOS. That syslog suite passed on Linux in earlier validation. Full local repository validation is not green, and E2E was not rerun for this documentation revision.
Earlier chart renders confirmed DaemonSet, central Deployment, and central Deployment-only topologies with store-owning components disabled. Earlier 5M-row candidate-query measurements above exclude the selected guard. No production cleanup, reader bookkeeping, runtime schema migration, Helm value, or dependency change is delivered here. Implementation follows maintainer acceptance and #2233.
Checklist
Self-review completed
Documentation updated (if needed)
Ready for review
Summary by CodeRabbit
Documentation
Added a proposed PostgreSQL changelog-retention design and protocol covering cleanup eligibility, bounded deletion, safety safeguards, configuration, metrics, and operational guidance.
Documented how retention age, saved consumer positions, and a prior-snapshot guard constrain cleanup, and that unsafe or unreadable state can block deletion.
Noted that cleanup is disabled by default, requires acknowledgment-safe consumers and a specified index, and is not implemented; retention remains a proposal.
This addresses CodeRabbit thread 4448095083 with protocol changes only. With retention enabled, MarkProcessed fails closed when changed_at cannot be verified. An empty or incomplete token table no longer authorizes deletion. Every PostgreSQL watcher construction path persists a database-clock start pair before returning a watcher. That covers three constructors through one shared helper. Start and the token schema are unchanged. Legacy-token failures fail closed and never overwrite the existing row. Operator recovery and acceptance cases are documented. The age and previous-snapshot guards are unchanged. Local link, wrapping and whitespace checks pass. The full make lint-test-all gate was not rerun for this documentation-only revision.
…hangelog
The PostgreSQL datastore_changelog is never trimmed (NVIDIA#2170). Propose a
batched cleaner in the store-client PostgreSQL provider that deletes a
row only when it is older than a configured retention and before the
oldest saved consumer position, compared as (changed_at, id). Stale
tokens stay in the bound and raise an alert. Off by default; open
questions are listed for maintainers.
Refs NVIDIA#2170
Signed-off-by: Sumedh Aerram <saerram@ucsb.edu>
It looks like this branch is under active development. To avoid overwhelming you with review comments due to an influx of new commits, CodeRabbit has automatically paused this review. You can configure this behavior by changing the reviews.auto_review.auto_pause_after_reviewed_commits setting.
The PR adds proposed ADR-068 and a PostgreSQL changelog-retention protocol. The documents specify opt-in cleanup, deletion bounds, transaction-horizon safeguards, acknowledgment-safe checkpoints, and operating requirements. The ADR index links to the proposal. No cleaner implementation is delivered.
Changes: Changelog retention proposal
Layer / File(s)
Summary
Cleanup bounds and execution docs/designs/README.md, docs/designs/068-postgresql-changelog-retention.md, docs/postgresql-changelog-retention-protocol.md
The proposal defines retention-age and saved-position bounds, cleaner ownership, advisory-lock coordination, transaction-horizon validation, and bounded deletion. The ADR lists proposed configuration, metrics, and tests.
Consumer checkpoints and rollout safeguards docs/designs/068-postgresql-changelog-retention.md, docs/postgresql-changelog-retention-protocol.md
The protocol specifies token handling, acknowledgment-safe checkpoints, conservative idle advancement, and reader-rollout requirements.
Operations and validation docs/designs/068-postgresql-changelog-retention.md, docs/postgresql-changelog-retention-protocol.md
The documents describe rollout conditions, rejected alternatives, and PostgreSQL references. The protocol states that cleanup does not run VACUUM or shrink the table file, and describes space-reclamation options.
NVIDIA/NVSentinel#2170: The proposal describes bounded cleanup for the reported changelog growth, but does not implement the cleaner.
NVIDIA/NVSentinel#2171: The protocol describes transaction-horizon safeguards relevant to cleanup blocked by long-open transactions.
Possibly related PRs
NVIDIA/NVSentinel#2233: This PR adds the resume index that the proposed bounded deletion query requires.
NVIDIA/NVSentinel#1550: Its checkpoint behavior relates to the saved consumer positions used to bound deletion.
Suggested labels:area/docs, size/L
Suggested reviewers:kaivalyamdabhadkar
Merge Risk: Low · previous review e2f09
This PR only proposes a design, so nothing changes at runtime. Before the design is accepted, the protocol should require checkpoints to fail closed when an event timestamp cannot be verified, and should not treat an empty resume-token table as proof that no consumer still needs history.
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The title clearly and concisely identifies the proposal of ADR-068 for bounded PostgreSQL changelog retention, which is the main change in the pull request.
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Inline comments:
Review comments at @docs/designs/068-postgresql-changelog-retention.md:
- Line 31: Update the PostgreSQL client-factory retention lifecycle so
client-factory-only deployments have a cleaner owner, or fail or alert when
DATASTORE_CHANGELOG_RETENTION is configured without one. Verify this behavior
across supported chart topologies, including when the listed cleaner-owning
components are disabled.
- Line 144: Update the “Long write transactions” discussion in the PostgreSQL
changelog-retention design to state that idle-session and statement timeouts do
not bound transaction lifetime, so an old row may be deleted before the NOTIFY
fetch. Describe this as an unresolved limitation and require a commit-time or
transaction-age guard before the cleaner can delete rows.
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The negative-age concern is addressed in 6e1681b6, and e2f09ad2 syncs current main without changing that proposal. The review was automatically paused before the negative-age revision; please review the current head once. Scoped PostgreSQL evidence and full-gate platform limitations are recorded in the PR description and reviewer reply.
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Summary
Refs #2170. This proposes ADR-068 for maintainers to decide. It does not implement it.
With the PostgreSQL datastore, nothing deletes from
datastore_changelog, so it grows without limit. The report in #2170 shows 42M rows and 90 GB on a ~350-node cluster. Thecleanup_changelog()function indocs/postgresql-schema.sqlis never called, and the components do not create it.AGENTS.md asks for an ADR before deleting event-store history on a timer, so this PR proposes the design first. The main points:
processedis not safe.MarkProcessedmarks an id prefix for the whole table, for all consumers. Socleanup_changelog()and the workaround in the issue can delete rows another consumer has not read.(changed_at, id)pair, plus the retention, checked on every deleted row. An id alone is not a position, because the poll orders by(changed_at, id)and ids follow allocation order, not time.last_updateddoes not prove that a consumer is gone.idx_changelog_resume_allfrom fix(store-client): add a changelog index the PostgreSQL change stream poll can use #2233. It is off by default, with new keys, variables and metrics only.The revised proposal selects a previous-snapshot guard: each run records
pg_snapshot_xmin(pg_current_snapshot())and only uses a horizon observed at least one cleanup interval earlier. A new optionalchangelog_cleanup_statetable shares the full horizon and observation time across owners. The first run seeds it without deleting. Comparisons account for 32-bit rowxminversusxid8; the bounded candidate query checks current row versions after validating the horizon window. No commit-timestamp server setting or older-writer change is required.The revision also includes acknowledgment-safe idle checkpoints for healthy quiet consumers, with unchanged consumer interfaces and resume-token fields. Idle advancement now requires a fresh activity inspection with no other open or prepared transactions and no hidden activity, followed by a new read snapshot. Its actual candidate pair must precede the inspection fence, and all handed-out deliveries must be acknowledged. Missing visibility or uncertain timestamp ordering defers idle progress; busy databases can conservatively hold cleanup back. Reader rollout is an explicit prerequisite before enabling cleanup; older readers cannot be identified automatically from the unchanged token format.
Invalid retention or cleanup settings warn and disable only the cleaner, without failing startup or ingestion. Seven days is
168h; Go does not accept7d.The detailed proposed guard and checkpoint protocol is separate to keep the ADR under the reading limit.
Alternatives considered: a Helm CronJob, calling
cleanup_changelog(), deleting inMarkProcessed, ignoring stale tokens, and partitioning. The open questions for maintainers are in the Notes section: the default, and how to recover from a removed component's token.Earlier measurements checked the candidate age-and-position query on PostgreSQL 16 with a 5M-row changelog and
idx_changelog_resume_all. These measurements exclude the selected long-transaction guard; they do not validate a complete cleaner:(10:00, id 200), the pair bound keeps a row at(10:05, id 150)and a young row with id 120. A bound onidalone would delete both.The negative-age review follow-up requires a new short repeatable-read transaction per delete batch, an assigned anchoring xid and the existing validated previous horizon. The guard permits snapshot-visible negative-age versions as well as versions strictly older than the horizon. This prevents a very old frozen prefix from permanently blocking cleanup. Both branches remain behind the retention and consumer-position conditions. Concurrent changes causing serialization failure roll back the entire batch; metrics count committed deletes only. Read committed is not permitted for this predicate.
Type of Change
Component(s) Affected
Testing
Final branch sync
e2f09ad2includes main152425f3without changing the ADR, protocol or index content. Relative to main this PR still changes only three documentation files. Local links, document lengths and whitespace checks pass. The required full gate on the synced revision again passed protobuf, license, module, Renovate, dead-code and unused-code checks, then stopped at the same four Linux boot-ID tests on macOS (339 tests, four failures). Full local validation remains incomplete; this sync does not claim a new runtime or E2E result.Latest revision
6e1681b6addresses the negative-age concern. On PostgreSQL 16, explicit synthetic old raw-XID cases cover signed-age boundaries and bounded progress through a modeled negative-age prefix. Separate real-row MVCC tests preserve late root/subtransaction/prepared commits and processed updates, exclude a post-snapshot negative-age insert under repeatable read, demonstrate why read committed is unsafe, and verify40001rolls back earlier deletes in the same batch. The prefix fixture uses a separate xid column, not physical ancient tuple headers. A live old-tuple/full-wrap acceptance test remains outstanding before release.An offline counter-advance fixture failed setup and was abandoned after automatic approval review rejected another retry under the repository retry limit. It is not counted as passing evidence. The ordinary MVCC container was disposed of.
Documentation links, structure, whitespace and lengths pass (ADR 2,993 words, protocol 1,483).
make lint-test-allran on6e1681b6: protobuf, license, module, Renovate, dead-code and unused-code checks passed, then the same four Linux boot-ID tests failed on macOS (339 tests, four failures). No assertions were weakened; full local validation is not green. No runtime cleaner or new E2E pass is claimed.Earlier documentation revision
82ae888aaddresses the late-commit idle-checkpoint finding. A fresh, network-isolated PostgreSQL 16 prototype reproduced the unsafe saved-tail loss, then passed the proposed conservative fence checks for xid-less/read-only writers, prepared transactions, activity-to-prepare transitions, disabled tracking, hidden visibility and a late no-listener commit returned by subsequent polling. This is SQL-prototype evidence; provider acknowledgment bookkeeping, arbitrary database clock-regression handling and full concurrency/restart release tests remain implementation prerequisites. The new protocol explicitly requires timestamp ordering and defers progress when it cannot be established.Final ADR/protocol links, structure, whitespace and lengths pass (2,985 / 1,326 words). Ran
make lint-test-allon82ae888awith the corrected isolated tools: protobuf, license, module, Renovate, dead-code and unused-code checks passed; the same four Linux boot-ID syslog tests failed on macOS (339 tests, four failures). No assertions were weakened. The complete local gate is not green. No runtime code or E2E result is claimed by this revision.Merge follow-up
71ce3fafbrings the branch up to main6ebbc1bd. The only conflict was the ADR index; both ADR-066 and ADR-068 entries are preserved. The proposal and protocol content are unchanged. Local links, ADR structure, document length, index entries and whitespace checks passed. After correcting the isolated Python tool environment to the current protobuf pin,make lint-test-allpassed protobuf, license, module, Renovate, dead-code and unused-code checks, then stopped at the same four Linux boot-ID tests on macOS (339 syslog tests, four failures). No assertions were weakened. Full local validation remains incomplete; E2E was not rerun for this index-only conflict resolution.This is a proposed design, not a cleaner implementation. Validation for
0556cc2a:VACUUM FREEZE. A later horizon made previously protected rows eligible. Observation times were advanced to model elapsed cleanup intervals.0, negative, below-minimum,24h,168h,7d, malformed and overflowing. Startup/ingestion behavior is an acceptance requirement, not implemented code tested by this documentation PR.make lint-test-allonce in the clean isolated revision checkout. Protobuf, license, module, Renovate, dead-code and unused-code gates passed; it stopped at four syslog tests requiring Linux/proc/sys/kernel/random/boot_id, absent on macOS. That syslog suite passed on Linux in earlier validation. Full local repository validation is not green, and E2E was not rerun for this documentation revision.Earlier chart renders confirmed DaemonSet, central Deployment, and central Deployment-only topologies with store-owning components disabled. Earlier 5M-row candidate-query measurements above exclude the selected guard. No production cleanup, reader bookkeeping, runtime schema migration, Helm value, or dependency change is delivered here. Implementation follows maintainer acceptance and #2233.
Checklist
Summary by CodeRabbit
Checkpoint verification follow-up (
36149d9c..90bb3b6b)This addresses CodeRabbit thread 4448095083 with protocol changes only. With retention enabled,
MarkProcessedfails closed whenchanged_atcannot be verified. An empty or incomplete token table no longer authorizes deletion. Every PostgreSQL watcher construction path persists a database-clock start pair before returning a watcher. That covers three constructors through one shared helper.Startand the token schema are unchanged. Legacy-token failures fail closed and never overwrite the existing row. Operator recovery and acceptance cases are documented. The age and previous-snapshot guards are unchanged. Local link, wrapping and whitespace checks pass. The fullmake lint-test-allgate was not rerun for this documentation-only revision.