On 31 May 2011, at 23:03, Dan Kuebrich wrote: > I think perhaps OP meant O(N * M), where N is number of rows and M is total > bytes.
That's probably more accurate. This is what it was doing: Say I repeatedly append 100 bytes to the same 1000 records. First time around that's 100,000 bytes to transfer. Second time around it has to read the first 100k, then write it back, plus the next 100k, making 300k. Next time it's read 200k, write 200k+100k, making 500k. After 100 iterations you're transferring 20Mb for a 100k update. MySQL really does do this; It's very painful. In my real case a 50 byte update to 500k records went from taking a few seconds to several hours, with no prospect of ever improving. Marcus
