Cleanup Concurrent RepositoryData Loading #48329
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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 elastic#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 elastic#48122
original-brownbear
added
>bug
:Distributed/Snapshot/Restore
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Pinging @elastic/es-distributed (:Distributed/Snapshot/Restore) |
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I didn't yet get around to a full test run here, so if this doesn't yet go green please hold off reviewing till I can fix the tests I may have missed :) |
| @@ -812,9 +812,6 @@ public void endVerification(String seed) { | |||
| public RepositoryData getRepositoryData() { | |||
| try { | |||
| return getRepositoryData(latestIndexBlobId()); | |||
| } catch (NoSuchFileException ex) { | |||
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There is no good reason to catch here or below. We break out on generation -1 and return empty data so whenever we fail to find data for gen. >= 0 it's a problem and we mustn't ignore it.
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Jup, this is not entirely unsurprisingly failing some REST tests: -> WIP EDIT: #46250 fixed the tests here sort of by accident by changing the order of shard and root level meta updates :) -> should be good to review now |
tlrx
approved these changes
Oct 23, 2019
| @@ -925,9 +922,6 @@ private RepositoryData getRepositoryData(long indexGen) { | |||
| repositoryData = RepositoryData.snapshotsFromXContent(parser, indexGen); | |||
| } | |||
| return repositoryData; | |||
| } catch (NoSuchFileException ex) { | |||
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nit: while we are at it, there are unneeded Long.toString() and local variable repositoryData usages
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I can't find it right now, but others disagreed with removing the Long.toString in another PR :( But yea let's clean up the redundant locals :)
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Thanks Tanguy! |
original-brownbear
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Oct 23, 2019
Just like elastic#48329 (and using the changes) in that PR we can run into a concurrent repo modification that we will throw on and must retry until consistent handling of this situation is implemented. Closes elastic#47384
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original-brownbear
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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 elastic#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 elastic#48122
original-brownbear
added a commit
to original-brownbear/elasticsearch
that referenced
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Nov 2, 2019
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 elastic#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 elastic#48122
original-brownbear
added a commit
to original-brownbear/elasticsearch
that referenced
this pull request
Nov 2, 2019
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 elastic#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 elastic#48122
original-brownbear
added a commit
to original-brownbear/elasticsearch
that referenced
this pull request
Nov 2, 2019
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 elastic#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 elastic#48122
original-brownbear
added a commit
that referenced
this pull request
Nov 2, 2019
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
original-brownbear
added a commit
that referenced
this pull request
Nov 2, 2019
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
This was referenced Feb 3, 2020
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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.
I would suggest back porting this all the way since it can theoretically have
repository corrupting effects on S3.
Fixes #48122