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d866803818
This commit adds a fast-path to the BITOP that can be used for all the bytes from 0 to the minimal length of the string, and if there are at max 16 input keys. Often the intersected bitmaps are roughly the same size, so this optimization can provide a 10x speed boost to most real world usages of the command. Bytes are processed four full words at a time, in loops specialized for the specific BITOP sub-command, without the need to check for length issues with the inputs (since we run this algorithm only as far as there is data from all the keys at the same time). The remaining part of the string is intersected in the usual way using the slow but generic algorith. It is possible to do better than this with inputs that are not roughly the same size, sorting the input keys by length, by initializing the result string in a smarter way, and noticing that the final part of the output string composed of only data from the longest string does not need any proecessing since AND, OR and XOR against an empty string does not alter the output (zero in the first case, and the original string in the other two cases). More implementations will be implemented later likely, but this should be enough to release Redis 2.6-RC4 with bitops merged in. Note: this commit also adds better testing for BITOP NOT command, that is currently the faster and hard to optimize further since it just flips the bits of a single input string. |
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