Re: Logical log write volumes

In article n4s@cix.compulink.co.uk, onlinedbc@cix.compulink.co.uk ("Malcolm Weallans") writes: >Andy Kent writes:- >> Can anyone tell me how you work out how much gets written to the logical >> logs during an insert-intensive application? What are the differenc >> here between buffered and unbuffered logging? (I thought buffered d >> "piggyback" writes, but I was on a site recently where the logging mode >> didn't seem to make any difference to logging volumes) >Andy, if you want to work out the contents for logical logs for a >particualr transaction you can use tbcheck to get the details of the >transaction. That's `tblog' (or onlog for the DSA inclined). > This tells you how much space in the logs are used for each >component of the transaction. As to your question concerning the >difference between buffered and unbuffered logging, I can't believe you >had to ask. The amount of logging does not change, merely the frequency >of flushing the buffer to disk. Buffered logging does leave some data >vulnerable that is all. The difference is in the page usage. The minimum unit of log I/O is a page. With unbuffered logging, as soon as you COMMIT, you write out the current buffer. Even if your buffer only has a BEGIN, DELETE, COMMIT in it then you will flush a whole page out to disk. With buffered logging the rest of the page after the COMMIT can be filled with further transactions. The ammount of log data is the same, only the packing of data within the pages is different. >Might I recommend that you get yourself on a decent Online course! Steady on! Cosmo