Performance of streaming with xsl:fork/xsl:for-each-group/@group-by
Although bug #3281 is now fixed, investigation of the bug showed a performance problem with streamed group-by. Specifically, there will be a Watch registered with the WatchManager every time a new group is encountered, and on each startElement() event, the WatchManager will go through this list of Watches sequentially to determine which of them match. Most of them won't match, but the cost of this search will increase with the number of groups, so applications involving a very large number of groups will become very inefficient.
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