Specialize pre-closing checks for engine implementations (#38702) #38727
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… ReadOnlyEngines (elastic#37426) Since version 6.7.0 the Close Index API guarantees that all translog operations have been correctly flushed before the index is closed. If the index is reopened as a Frozen index (which uses a ReadOnlyEngine) we can verify that the maximum sequence number from the last Lucene commit is indeed equal to the last known global checkpoint and refuses to open the read only engine if it's not the case. In this PR the check is only done for indices created on or after 6.7.0 as they are guaranteed to be closed using the new Close Index API. Related elastic#33888
The Close Index API has been refactored in 6.7.0 and it now performs pre-closing sanity checks on shards before an index is closed: the maximum sequence number must be equals to the global checkpoint. While this is a strong requirement for regular shards, we identified the need to relax this check in the case of CCR following shards. The following shards are not in charge of managing the max sequence number or global checkpoint, which are pulled from a leader shard. They also fetch and process batches of operations from the leader in an unordered way, potentially leaving gaps in the history of ops. If the following shard lags a lot it's possible that the global checkpoint and max seq number never get in sync, preventing the following shard to be closed and a new PUT Follow action to be issued on this shard (which is our recommended way to resume/restart a CCR following). This commit allows each Engine implementation to define the specific verification it must perform before closing the index. In order to allow following/frozen/closed shards to be closed whatever the max seq number or global checkpoint are, the FollowingEngine and ReadOnlyEngine do not perform any check before the index is closed. Co-authored-by: Martijn van Groningen <martijn.v.groningen@gmail.com>
tlrx
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:Distributed Indexing/Engine
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Pinging @elastic/es-distributed |
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Backport of #37426 and #38702 to
6.7.