Hi Tom, > I was profiling a case involving UPDATEs into a table with too many indexes (brought to > mind by mysql's sql-bench, about which more later) and got this rather surprising result > for routines costing more than 1% of the total runtime:
(cut) > I suppose that the bulk of the CPU cycles being attributed to XLogInsert are going into > the inlined CRC calculations. Maybe we need to think twice about the cost/benefit ratio > of using 64-bit CRCs to protect xlog records that are often only a few dozen bytes. Wow, a 64-bit CRC does seem excessive, especially when going back to Zmodem days where a 50-100k file seemed to be easily protected by a 32-bit CRC. I'm sure there are some error rates somewhere dependent upon the polynomial and the types of error detected.... Try the following link towards the bottom: http://www.ee.unb.ca/tervo/ee4253/crc.htm for some theory on detection rates vs. CRC size. Kind regards, Mark. ------------------------ WebBased Ltd South West Technology Centre Tamar Science Park Plymouth PL6 8BT T: +44 (0)1752 791021 F: +44 (0)1752 791023 W: http://www.webbased.co.uk ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq