2016-09-11 9:23 GMT+02:00 dandl <da...@andl.org>: > *From:* pgsql-general-ow...@postgresql.org [mailto:pgsql-general-owner@ > postgresql.org] *On Behalf Of *Pavel Stehule > > I guess my question then is: how much do you pay for that durability? If > you benchmark Postgres configured for pure in-memory usage with absolutely > no writes to disk (or SSD or network), where is it spending its time? Is > there a lot of overhead in getting data in and out of cache buffers and > conversions and in concurrency control? > > > > It is not about durability only. > > Postgres holds data in format equal or similar to saved data on persistent > storage. There are repeated serialization and deserialization. Some > structures are designed to be simply saved (like Btree), but the > performance is second target. > > I believe so new memory databases can be 10-100x faster - depends on use > case, because they hold data primary in memory and uses different data > structures. The performance of these databases is great, when all data are > well placed in memory all time. But the performance is pretty bad, when > this rule is not true. There is another issue - when you increase speed of > database write operations, probably you will hit a file system limits, spin > lock issues - so it is one reason, why big system are based on distributed > systems more and more. > > That’s the point I’m making, exactly. The question is: does anyone have a > handle on how big that cost really is, as a guide to whether to try to do > anything about it? Is it really 25x as Stonebraker says? >
Some years ago the MonetDB developers did comparing with C++ applications. The cost of generic database is difference of speed between generic database and native C application. I did some benchmarks of MonetDB and it is really pretty fast for OLAP. You can try to implement TPC-B benchmark in C (without SQL - the cost of SQL is not significant), and you can check it. Regards Pavel > > > Regards > > David M Bennett FACS > *------------------------------* > > *Andl - A New Database Language - andl.org <http://andl.org>* > > > > > > >
