Mladen Gogala <mladen.gogala@vmsinfo.com> wrote:
> create a definitive bias toward one type of the execution plan.
We're talking about trying to support the exact opposite. This all
started because a database which was tuned for good response time
for relatively small queries against a "hot" portion of some tables
chose a bad plan for a weekend maintenance run against the full
tables. We're talking about the possibility of adapting the cost
factors based on table sizes as compared to available cache, to more
accurately model the impact of needing to do actual disk I/O for
such queries.
This also is very different from trying to adapt queries to what
happens to be currently in cache. As already discussed on a recent
thread, the instability in plans and the failure to get to an
effective cache set make that a bad idea. The idea discussed here
would maintain a stable plan for a given query, it would just help
choose a good plan based on the likely level of caching.
-Kevin
