Realtime get from in-memory segment when possible #64504
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dnhatn
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Pinging @elastic/es-distributed (:Distributed/Engine) |
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Thanks @dnhatn , this looks good. I have only looked at the main part of the PR for now and have a single comment/question.
server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java
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server/src/main/java/org/elasticsearch/index/shard/IndexShard.java
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server/src/main/java/org/elasticsearch/index/engine/SingleDocDirectoryReader.java
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| @Override | ||
| public CacheHelper getReaderCacheHelper() { | ||
| return in.getReaderCacheHelper(); |
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Might mostly be for my understanding, but since the wrapped directory reader could return different results from the inner reader, should we not return null here?
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Good catch. We should return null here as we modify the liveDocs. I addressed it in eb968e4.
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I had to reverted this and added a comment instead. Please see: e176bf2
jpountz
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server/src/main/java/org/elasticsearch/index/engine/Engine.java
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@henningandersen Are you okay with the latest changes? |
henningandersen
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Nov 9, 2020
server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
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@henningandersen @jpountz Thanks for your reviews. |
dnhatn
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If the reader wrapper is specified, then we can't perform a realtime get using operations from translog. With this change, we will create an in-memory Lucene segment from that indexing operation and perform a realtime get from that segment to avoid refresh storms.
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Reading from translog during a realtime get requires special handling in some higher level components, e.g. ShardGetService, where we're doing a bunch of tricks to extract other stored fields from the source. Another issue with the current approach relates to #74227 where we introduce a new "field usage tracking" directory wrapper that's always applied, and we want to make sure that we can still quickly do realtime gets from translog without creating an in-memory index of the document, even when this directory wrapper exists. This PR introduces a directory reader that contains a single translog indexing operation. This can be used during a realtime get to access documents that haven't been refreshed yet. In the normal case, all information relevant to resolve the realtime get is mocked out to provide fast access to _id and _source. In case where more values are requested (e.g. access to other stored fields) etc., this reader will index the document into an in-memory Lucene segment that is created on-demand. Relates #64504
ywelsch
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Reading from translog during a realtime get requires special handling in some higher level components, e.g. ShardGetService, where we're doing a bunch of tricks to extract other stored fields from the source. Another issue with the current approach relates to #74227 where we introduce a new "field usage tracking" directory wrapper that's always applied, and we want to make sure that we can still quickly do realtime gets from translog without creating an in-memory index of the document, even when this directory wrapper exists. This PR introduces a directory reader that contains a single translog indexing operation. This can be used during a realtime get to access documents that haven't been refreshed yet. In the normal case, all information relevant to resolve the realtime get is mocked out to provide fast access to _id and _source. In case where more values are requested (e.g. access to other stored fields) etc., this reader will index the document into an in-memory Lucene segment that is created on-demand. Relates #64504
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If the reader wrapper is specified, then we can't perform a realtime get using operations from translog. With this change, we will create an in-memory Lucene segment from that indexing operation and perform a realtime get from that segment to avoid refresh storms.