Always use DirectoryReader for realtime get from translog#74722
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ywelsch merged 7 commits intoelastic:masterfrom Jul 1, 2021
Merged
Always use DirectoryReader for realtime get from translog#74722ywelsch merged 7 commits intoelastic:masterfrom
ywelsch merged 7 commits intoelastic:masterfrom
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ywelsch
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Jun 30, 2021
| IndexReader.CacheHelper cacheHelper = reader.getReaderCacheHelper(); // this one takes deletes into account | ||
| if (cacheHelper == null) { | ||
| throw new IllegalStateException("Reader " + reader + " does not support caching"); | ||
| return computeNumDocs(reader, roleQueryBits); |
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This change was necessary as DocumentSubsetReader was a bad citizen. It required the leafreader that it wrapped to have a readerCacheHelper, but then at the same time did not expose a reader cache helper by its own wrapping leafreader, so essentially double-standards.
I don't see a reason for this reader not to work when caching isn't available (single-document case)
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Pinging @elastic/es-distributed (Team:Distributed) |
dnhatn
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Jun 30, 2021
server/src/main/java/org/elasticsearch/index/mapper/DocumentLeafReader.java
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henningandersen
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Jul 1, 2021
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LGTM.
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server/src/main/java/org/elasticsearch/index/engine/Engine.java
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server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java
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server/src/main/java/org/elasticsearch/index/engine/TranslogDirectoryReader.java
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ywelsch
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Jul 1, 2021
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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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