Skip final reduction if SearchRequest holds a cluster alias #37000
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With elastic#36997 we added the ability to provide a cluster alias with a SearchRequest. The next step is to disable the final reduction whenever a cluster alias is provided with the SearchRequest. A cluster alias will be provided when executing a cross-cluster search request with alternate execution mode, where each cluster does its own reduction locally. In order for the CCS node to be able to later perform an additional reduction of the results, we need to make sure that all the needed info stays available. This means that terms aggregations can be reduced but not pruned, and pipeline aggs should not be executed. The final reduction will happen later in the CCS coordinating node. Relates to elastic#36997 & elastic#32125
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@jimczi this is now ready for review ;) |
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Dec 28, 2018
With elastic#36997 and elastic#37000 we added the ability to provide a cluster alias with a SearchRequest and to perform non-final reduction when a cluster alias is set to the incoming search request. With CCS soon supporting local reduction on each remote cluster, we also need to prevent shard_size of terms aggs to be adjusted on the data nodes. We may end up querying a single shard per cluster, but later we will have to reduce results coming from multiple cluster hence we still have to collect more buckets than needed to guarantee some level of precision. This is done by adding the ability to override the shard_size on the coordinating node as part of the rewrite phase. This will be done only when searching against multiple clusters, meaning when using CCS with alternate execution mode. Setting the shard_size explicitly on the coord node means that it will not be overridden later on the data nodes. The shard_size will still be set on the data nodes like before in all other cases (local search, or CCS with ordinary execution mode). Relates to elastic#32125
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With #36997 we added the ability to provide a cluster alias with a SearchRequest. The next step is to disable the final reduction whenever a cluster alias is provided with the SearchRequest. A cluster alias will be provided when executing a cross-cluster search request with alternate execution mode, where each cluster does its own reduction locally. In order for the CCS node to be able to later perform an additional reduction of the results, we need to make sure that all the needed info stays available. This means that terms aggregations can be reduced but not pruned, and pipeline aggs should not be executed. The final reduction will happen later in the CCS coordinating node. Relates to #36997 & #32125
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Jan 31, 2019
WIth elastic#37000 we made sure that fnial reduction is automatically disabled whenever a localClusterAlias is provided with a SearchRequest. While working on elastic#37838, we found a scenario where we do need to set a localClusterAlias yet we would like to perform a final reduction in the remote cluster: when searching on a single remote cluster. This commit adds support for a separate finalReduce flag to SearchRequest and makes use of it in TransportSearchAction in case we are searching against a single remote cluster. This also makes sure that num_reduce_phases is correct when searching against a single remote cluster: it makes little sense to return `num_reduce_phases` set to `2`, which looks especially weird in case the search was performed against a single remote shard. We should perform one reduction phase only in this case and `num_reduce_phases` should reflect that.
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With #37000 we made sure that fnial reduction is automatically disabled whenever a localClusterAlias is provided with a SearchRequest. While working on #37838, we found a scenario where we do need to set a localClusterAlias yet we would like to perform a final reduction in the remote cluster: when searching on a single remote cluster. Relates to #32125 This commit adds support for a separate finalReduce flag to SearchRequest and makes use of it in TransportSearchAction in case we are searching against a single remote cluster. This also makes sure that num_reduce_phases is correct when searching against a single remote cluster: it makes little sense to return `num_reduce_phases` set to `2`, which looks especially weird in case the search was performed against a single remote shard. We should perform one reduction phase only in this case and `num_reduce_phases` should reflect that. * line length
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With #36997 we added the ability to provide a cluster alias with a SearchRequest.
The next step is to disable the final reduction whenever a cluster alias is provided. A cluster alias will be provided when executing a cross-cluster search request with alternate execution mode, where each cluster does its own reduction locally. In order for the CCS node to be able to later perform an additional reduction of the results, we need to make sure that there is all the needed info available. This means that terms aggregations can be reduced but not pruned, and pipeline aggs should not be executed. The final reduction will happen in the CCS coordinating node.
Relates to #36997 & #32125