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From Marcus Bointon <mar...@synchromedia.co.uk>
Subject Re: Appending to fields
Date Wed, 01 Jun 2011 01:36:40 GMT
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
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