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https://issues.apache.org/jira/browse/IOTDB-653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17104033#comment-17104033
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Wei Shao commented on IOTDB-653:
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Hi, I have implemented LAST query of single node. I'd like to work on this
issue.
> Separate LAST cache from MTree
> ------------------------------
>
> Key: IOTDB-653
> URL: https://issues.apache.org/jira/browse/IOTDB-653
> Project: Apache IoTDB
> Issue Type: Improvement
> Components: Core/Engine
> Reporter: Tian Jiang
> Priority: Major
> Labels: LAST, cluster, metadata
>
> Currently, we have a cache in MTree to store the LAST value of timeseries, in
> the distributed version, however, the metadata and data are stored
> separately, and when the metadata is needed, it will be pulled from another
> node and stored in a local cache, resulting in that such timeseries does not
> exist in MTree and its LAST cache is accessed, a PathNotExistException will
> be raised.
> So we temporarily disable the LAST cache of the remotely existing timeseries,
> but we hope we can modify it so that we can still cache the last value of
> those timeseries.
> Here is one possible solution: abstract a LastCacheManager to manage all last
> caches instead of storing them in MTree, so even when the timeseries does not
> exist locally, its last value can still be cached and visited.
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