7e4233746e
Allows index condition pushdown for reverse ordered scans, a previously disabled feature due to poor performance. This patch adds a new API to the handler class called set_end_range which allows callers to tell the handler what the end of the index range will be when scanning. Combined with a pushed index condition, the handler can scan the index efficiently and not read beyond the end of the given range. When checking if the pushed index condition matches, the handler will also check if scanning has reached the end of the provided range and stop if so. If we instead only enabled ICP for reverse ordered scans without also calling this new API, then the handler would perform unnecessary index condition checks. In fact this would continue until the end of the index is reached. These changes are agnostic of storage engine. That is, any storage engine that supports index condition pushdown will inhereit this new behavior as it is implemented in the SQL and storage engine API layers. The partitioned tables storage meta-engine (ha_partition) adds an override of set_end_range which recursively calls set_end_range on its child storage engine (handler) implementations. This commit updates the test made in an earlier commit to show that ICP matches happen for the reverse ordered case. This patch is based on changes written by Olav Sandstaa in MySQL commit da1d92fd46071cd86de61058b6ea39fd9affcd87
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