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Posted to issues@iceberg.apache.org by "raghavyadav01 (via GitHub)" <gi...@apache.org> on 2026/10/22 17:13:35 UTC
[PR] Docs: Clarify that isolation-level properties do not apply to appends [iceberg]
raghavyadav01 opened a new pull request, #18613:
URL: https://github.com/apache/iceberg/pull/18613
Closes #18608
The configuration page documents `write.delete.isolation-level`, `write.update.isolation-level` and `write.merge.isolation-level` without saying that they are scoped to row-level operations. Users setting them on append-heavy workloads reasonably expect fewer commit conflicts, which makes these properties a common wrong turn when diagnosing 409 `CommitFailedException` responses from a REST catalog.
The reporter's case was 5 tables written by ~30 independent Flink append jobs each, at roughly 27 commits per minute per table.
## Changes
**`docs/docs/configuration.md`** — adds note `[2]`, referenced from the three isolation-level rows, following the existing `[1]` convention used by the metrics-mode properties:
> Isolation levels apply only to row-level operations: DELETE, UPDATE and MERGE. Appends have no isolation level. Concurrent appends are resolved by commit retry rather than by a data conflict check, so these properties have no effect on append or INSERT.
**`docs/docs/reliability.md`** — adds a paragraph under *Retry validation* explaining *why*, so the two pages agree:
> Appends assume nothing about the data already in the table, so a conflicting commit never invalidates them and they are always safe to re-apply. This is why appends have no isolation level [...]
Docs only; no behaviour change. The three table rows differ from `main` by the ` [2]` marker alone — the column boundaries are unchanged.
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Re: [PR] Docs: Clarify that isolation-level properties do not apply to appends [iceberg]
Posted by "raghavyadav01 (via GitHub)" <gi...@apache.org>.
raghavyadav01 commented on PR #18613:
URL: https://github.com/apache/iceberg/pull/18613#issuecomment-6375626623
Fair question. @SergeyTimofeev1989 answered it on #18608: switching to `snapshot` did change something on his tables, just not the side he expected. Spark DELETEs mostly stopped failing with `Found conflicting files` while the Flink appends kept getting the same 409s. A property that visibly cuts conflicts for one writer is easy to read as cutting them generally.
His wording is also better than mine, because it says which side of a concurrent commit the property applies to:
> Applies only to the DELETE, UPDATE or MERGE command being committed: it controls whether data files added by concurrent commits (including appends) count as conflicts. It has no effect on how appends are committed.
Happy to swap that in, or close this if you would rather he carry it.
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Re: [PR] Docs: Clarify that isolation-level properties do not apply to appends [iceberg]
Posted by "RussellSpitzer (via GitHub)" <gi...@apache.org>.
RussellSpitzer commented on PR #18613:
URL: https://github.com/apache/iceberg/pull/18613#issuecomment-6354714160
Does this really need to be said? Aren't Delete, update and Merge obviously not append related? Why would a user changing these on append workloads assume that they would have fewer conflicts? I'm not sure I follow
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