Thank you. That works. Best, Alireza
On Tue, May 21, 2019 at 3:06 PM Stamatis Zampetakis <zabe...@gmail.com> wrote: > Hi Alireza, > > I suppose you mainly need count estimates for base tables. > One way to provide this information is by implementing the Table interface > [1] and providing an appropriate implementation for the getStatistic() > method. > Another way would be to extend TableScan [2] operator and provide another > implementation for computeSelfCost() method. > If you really need to pass your own provider you may find some information > in the RelMetadataTest [3]. > > Best, > Stamatis > > > [1] > > https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/schema/Table.java > [2] > > https://github.com/apache/calcite/blob/2765791e60c46e0d66a3c510a5c91d16fe757720/core/src/main/java/org/apache/calcite/rel/core/TableScan.java#L87 > [3] > > https://github.com/apache/calcite/blob/2765791e60c46e0d66a3c510a5c91d16fe757720/core/src/test/java/org/apache/calcite/test/RelMetadataTest.java#L1006 > > On Mon, May 20, 2019 at 6:55 PM Alireza Samadian > <asamad...@google.com.invalid> wrote: > > > Hi, > > > > I'm working on Beam SQL and we are using Apache Calcite for our query > > parsing and optimization. We are trying to use row count estimates for > > Volcano Optimizer. Currently, Calcite returns row count estimate of 100 > for > > every table. > > It seems the cost estimate comes from bunch of handlers in > > org.apache.calcite.rel.metadata.RelMetadataQuery; however, apparently the > > handlers are automatically generated and I cannot figure out how I can > pass > > my own handler for cost estimation. Also, I am not even sure if this is > the > > standard way of passing my own cost estimates. > > I found this thread in StackOverflow: > > > > > https://stackoverflow.com/questions/54726015/why-does-apache-calcite-estimates-100-rows-for-all-tables-a-query-contains/54739313#54739313 > > > > One of the replies suggests that the only way to inject cardinality > > estimates for tables is via an ExternalCatalog. I cannot find any > > information about ExternalCatalog and I am not sure even what it is. > > > > I will appreciate if someone guides me or send me some links or examples. > > > > Best, > > Alireza Samadian > > >
