If searching in all namespace then remove the namespace filters all together. We should probably do this using the namespace list rather than the actual all: prefix. If the list contains all active namespaces then we really don't need to filter. It just slows things down.
I wonder on a per-index basis so we don't filter if the index contains just that namespace.
I tested this on an "all" search and it cut the search time from about 100 millis to about 200 millis.
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