Right, I understand that, and read those explanations in various incarnations from other authors. But what has Oracle documented? The sections on ASSM only reference a single HWM. On Tue, May 6, 2008 at 10:29 AM, goran bogdanovic <goran00@xxxxxxxxx> wrote: > hi, > > It has to do with how oracle process new allocated blocks. In case when > hwm is moved forward, oracle does not immediately format all of the 'new' > blocks allocated...oracle make it on their first use. This means, when full > reading a segment, oracle somehow need to know if this blocks are formatted > and eligible to be read or not...means nothing interesting in them. > For that purpose there is low hwm and hwm (or hhwm). For all the blocks > which are between low hwm and hwm, when full scanning a segment, oracle have > to check assm bitmap block to see which blocks can be read and which can be > skipped. > > hth, > goran > > > > > On Tue, May 6, 2008 at 4:43 PM, Charles Schultz <sacrophyte@xxxxxxxxx> > wrote: > > > Broswing through various blogs, whitepapers and other presentations, I > > have seen folks like Tom Kyte and Lutz Hartman reference the HHWM and LHWM > > of ASSM tables, however I have been unable to find where they are officially > > documented. Perhaps this is a limitation of tahiti and metalink (metalink > > gave me one hit for bug 6416822). I have looked through the Concepts, > > New Features and DBA books in the documentation set, learning a lot in the > > process, and still have a lot to go back over. *grin* Additionally, I > > appreciate that dbms_space gives us access to detailed information about > > used blocks, but I find it a little odd that the HWM is not specifically > > included, much less HHWM and LHWM. Forgive me if I missed it, but did Oracle > > ever document these ASSM high water marks? > > > > Thanks to all of you who have worked hard to expose various internal > > tidbits and publish helpful hints. > > > > -- > > Charles Schultz > > > -- Charles Schultz