Cleanup Concurrent RepositoryData Loading (#48329)#48834
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original-brownbear merged 1 commit intoelastic:7.xfrom Nov 2, 2019
original-brownbear:48329-7.x
Merged
Cleanup Concurrent RepositoryData Loading (#48329)#48834original-brownbear merged 1 commit intoelastic:7.xfrom original-brownbear:48329-7.x
original-brownbear merged 1 commit intoelastic:7.xfrom
original-brownbear:48329-7.x
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The loading of `RepositoryData` is not an atomic operation. It uses a list + get combination of calls. This lead to accidentally returning an empty repository data for generations >=0 which can never not exist unless the repository is corrupted. In the test #48122 (and other SLM tests) there was a low chance of running into this concurrent modification scenario and the repository actually moving two index generations between listing out the index-N and loading the latest version of it. Since we only keep two index-N around at a time this lead to unexpectedly absent snapshots in status APIs. Fixing the behavior to be more resilient is non-trivial but in the works. For now I think we should simply throw in this scenario. This will also help prevent corruption in the unlikely event but possible of running into this issue in a snapshot create or delete operation on master failover on a repository like S3 which doesn't have the "no overwrites" protection on writing a new index-N. Fixes #48122
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Pinging @elastic/es-distributed (:Distributed/Snapshot/Restore) |
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The loading of
RepositoryDatais not an atomic operation.It uses a list + get combination of calls.
This lead to accidentally returning an empty repository data
for generations >=0 which can never not exist unless the repository
is corrupted.
In the test #48122 (and other SLM tests) there was a low chance of
running into this concurrent modification scenario and the repository
actually moving two index generations between listing out the
index-N and loading the latest version of it. Since we only keep
two index-N around at a time this lead to unexpectedly absent
snapshots in status APIs.
Fixing the behavior to be more resilient is non-trivial but in the works.
For now I think we should simply throw in this scenario. This will also
help prevent corruption in the unlikely event but possible of running into this
issue in a snapshot create or delete operation on master failover on a
repository like S3 which doesn't have the "no overwrites" protection on
writing a new index-N.
Fixes #48122
backport of #48329