We are trying to optimize a search routine for keys in fixed length rows in an unordered array. As the number of rows in the array grows, a serial search becomes relatively inefficient, so we looked for another technique. We tried a SEARCH STRING (SRST) against a one byte hash of the key to see if it could give us better performance. The relative positive of the matching byte in the SRST array was used to determine the location of the key in the original array; if the keys match, the row is found; if they don't match, we redrive the SRST. At about 50 rows, SRST is more efficient than a serial search so it justifies maintaining the hash array. On the average, we assume the SRST would have to be redriven about (n/256)/2 times, where n is the number of rows in the array. This would not be a big factor for several thousand rows, but as the number of rows went into the tens of thousands, we tried Search String Unicode (SRSTU). It appears to be identical to SRST, except it compares 2-byte values (at 2-byte boundaries). So we created a 2-byte hash and, using the same technique based on relative position, tested for performance improvements compared to SRST when the number of rows exceeded 10000. We thought that the reduction in the number of redrives due to non-matching keys (on average, (n/65536)/2) would more than offset the hash array doubling in size.
Our preliminary results show SRSTU about taking about 50-60% more time for 15000 and 25000 rows. That came as a surprise to us. We will do more testing. Is there a possibility we are encountering a hardware vs. microcode implementation of the instuctions? Has anyone else tested the performance of these instructions? Regards, Gary Gary Weinhold Senior Application Architect DATAKINETICS | Data Performance & Optimization Phone:+1.613.523.5500 x216 Email: weinh...@dkl.com Visit us online at www.DKL.com E-mail Notification: The information contained in this email and any attachments is confidential and may be subject to copyright or other intellectual property protection. If you are not the intended recipient, you are not authorized to use or disclose this information, and we request that you notify us by reply mail or telephone and delete the original message from your mail system.
