On 2018/06/20 16:21, Pavel Stehule wrote: > 2018-06-20 7:44 GMT+02:00 Amit Langote <langote_amit...@lab.ntt.co.jp>: > >> On 2018/06/02 0:15, Ashutosh Bapat wrote: >>> I think we should at least display "Type" as "partitioned table" for a >>> partitioned table, so that it's easy to understand why the size is 0; >>> partitioned tables do not hold any data by themselves. >> >> There was a long discussion last year (during PG 10 beta period), such as >> [1], and it seems most of us agreed to doing the above. Maybe, we should >> finally do it for PG 12, if not PG 11. >> >> Regarding showing the size of partitioned tables, there are many opinions >> and it's not clear if showing it in \dt itself is appropriate. For one, >> there is no pg_relation_size() or pg_table_size() equivalent in the >> backend for aggregating the size of all tables in a partition tree and I >> think people are not quite on board about having such a function in the >> backend [2]. > > Now, the number of partitions can be low, but if the Postgres can better > process high number of partitions, then for some tables we can have > hundreds partitions. > > Then usual \dt can be not too much usable. The aggregation can be done on > client side. But maybe this idea is premature. Now, for PG 12, we can start > with > > \dtP+ command for showing partition tables only with aggregate size via all > related partitions. > > Is it acceptable idea?
Do you mean \dt continues to show size 0 for partitioned tables, but with the new option (\dtP+) shows the actual size by aggregating across partitions? +1 to such a feature, but we need to agree on an acceptable implementation for that. How does the aggregation happen: 1. In a new dedicated function in the backend (parallel to pg_table_size)? or 2. psql issues a separate query to compute the total size of a partition tree For option 2, I had posted a patch that simplifies writing such a query and posted that here: https://www.postgresql.org/message-id/7a9c5328-5328-52a3-2a3d-bf1434b4dd1d%40lab.ntt.co.jp With that patch, the query to get the total size of a partition tree becomes as simple as: select sum(pg_table_size(p)) as size from pg_get_inheritance_tables('partitioned_table_name') p Thanks, Amit
