What is a “functional” versus an “indexed” lookup?
There are two ways the kernel can query the text index. In the first – and most common – case, the kernel asks the text index for all the rowids that satisfy a particular text search. These rowids are returned in blocks. In the second, the kernel passes individual rowids to the text index, and asks whether that particular rowid satisfies a certain text criterion. The second is known as a functional lookup, and is most commonly done where there is a very selective structured clause, so that only a few rowids must be checked against the text index.
There are two ways the kernel can query the text index. In the first and most common case, the kernel asks the text index for all the rowids that satisfy a particular text search. These rowids are returned in batches. In the second, the kernel passes individual rowids to the text index, and asks whether that particular rowid satisfies a certain text criterion. The second is known as a functional lookup, and is most commonly done where there is a very selective structured clause, so that only a few rowids must be checked against the text index.
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