Vova, what about maintaining the size as you go? This way you don't have to count multiple versions, no?
D. On Wed, Apr 25, 2018, 5:07 PM Vladimir Ozerov <voze...@gridgain.com> wrote: > This is interesting question. Full-scan size may be tremendously slow > operation on large data sets. On the other hand, printing total number of > tuples including old and aborted versions make little to no sense as well. > Looks like we need to choose lesser of two evils. What if we do the > following: > 1) Left default behavior as is - O(1) complexity, but includes invalid > versions > 2) As Sergey suggested, add new peek mode "MVCC_ALIVE_ONLY" which will > perform full scan. > > Alternatively we may throw an "UnsupportedOperationException" from this > method - why not? > > Thoughts? > > On Tue, Apr 24, 2018 at 4:28 PM, Sergey Kalashnikov <zkilling...@gmail.com > > > wrote: > > > Hi Igniters, > > > > I need your advice on a task at hand. > > > > Currently cache API size() is a constant time operation, since the > > number of entries is maintained as a separate counter. > > However, for MVCC-enabled cache there can be multiple versions of the > > same entry. > > In order to calculate the size we need to obtain a MVCC snapshot and > > then iterate over data pages filtering invisible versions. > > So, it is impossible to keep the same complexity guarantees. > > > > My current implementation internally switches to "full-scan" approach > > if cache in question is a MVCC-enabled cache. > > It happens unbeknown to users, which may expect lightning-fast > > response as before. > > Perhaps, we might add a new constant to CachePeekMode enumeration that > > is passed to cache size() to make it explicit? > > > > The second concern is that cache size calculation is also included > > into Cache Metrics API and Visor functionality. > > Will it be OK for metrics and things alike to keep returning raw > > unfiltered number of entries? > > Is there any sense in showing raw unfiltered number of entries which > > may vary greatly from invokation to invokation with just simple > > updates running in background? > > > > Please share your thoughts. > > > > Thanks in advance. > > -- > > Sergey > > >
