2018-02-26 9:56 GMT+01:00 Lætitia Avrot <laetitia.av...@gmail.com>: > Although VACUUM and VACUUM FULL is different, then result is same (depends >> on detail level) - the data files are optimized for other processing. You >> should to see a VACUUM like family of commands that does some data files >> optimizations. VACUUM, VACUUM FULL, VACUUM FREEZE, VACUUM ANALYZE, ... >> Personally I don't think so we need to implement new synonym command for >> this case. >> > > Here's how I understand what you wrote : "Each and every vacuum operations > are different flavours for files optimization so it's legitimate to use > similar names". I agree for VACUUM ANALYZE and VACUUM FREEZE that can be > seen as options to do more things than a simple VACUUM. > > But I disagree for VACUUM FULL that isn't an option to do one more thing > than VACUUM does. VACUUM FULL is a complete different process. > > Let's take an example: > In a production server with average production load, if you're already > running a VACUUM, you can change it to a VACUUM ANALYZE without many risks. > But I wouldn't dare try a VACUUM FULL without pg_repack. >
VACUUM and VACUUM ANALYZE does same VACUUM work. The VACUUM FREEZE is different too. > > >> Why you you cannot to say your students - "VACUUM FULL is like SHRINK in >> SQL Server"? >> > > I do explain that to my students but I'm not sure they memorize it, > because they do have a lot to memorize in a training session. > Maybe the core of this issue is fact so VACUUM FULL, VACUUM FREEZE is statements based on two keywords commands. Lazy VACUUM uses just keyword. >From this perspective the lazy VACUUM "should be" renamed, because it is inconsistent - and some databases uses some names like OPTIMIZE table (and it sound much more optimistic :)). I teach PostgreSQL more than ten years - and I have not the problem with this topic - the hard part is explain of VACCUM FREEZE - but VACUUM and VACUUM FULL can be explained simply (with some detail reduction). VACUUM recuces MVCC costs, VACUUM FULL reduces bloating. ANALYZE is orthogonal - calculate column statistic. > > I keep meeting customers to who I have to explain that a simple VACUUM > doesn't rebuild indexes. Am I the only one facing that problem ? > simple VACUUM (lazy VACUUM does a tasks that don't needs aggressive locks) - rebuild indexes needs strong locks. I agree, it is not pretty clean, because VACUUM FULL share some work with REINDEX, but introduction new command change nothing. > > >> Regards >> >> Pavel >> > > Regards > > Lætitia >
