2021年4月8日(木) 18:25 Fujii Masao <masao.fu...@oss.nttdata.com>: > > On 2021/04/08 15:48, Kohei KaiGai wrote: > > 2021年4月8日(木) 15:04 Fujii Masao <masao.fu...@oss.nttdata.com>: > >> > >> On 2021/04/08 13:43, Kohei KaiGai wrote: > >>> In case when a local table (with no children) has same contents, > >>> TRUNCATE command > >>> witll remove the entire table contents. > >> > >> But if there are local child tables that inherit the local parent table, > >> and TRUNCATE ONLY <parent table> is executed, only the contents in the > >> parent will be truncated. I was thinking that this behavior should be > >> applied to the foreign table whose remote (parent) table have remote child > >> tables. > >> > >> So what we need to reach the consensus is; how far ONLY option affects. > >> Please imagine the case where we have > >> > >> (1) local parent table, also foreign table of remote parent table > >> (2) local child table, inherits local parent table > >> (3) remote parent table > >> (4) remote child table, inherits remote parent table > >> > >> I think that we agree all (1), (2), (3) and (4) should be truncated if > >> local parent table (1) is specified without ONLY in TRUNCATE command. > >> OTOH, if ONLY is specified, we agree that at least local child table (2) > >> should NOT be truncated. > >> > > My understanding of a foreign table is a representation of external > > data, including remote RDBMS but not only RDBMS, > > regardless of the parent-child relationship at the local side. > > So, once a local foreign table wraps entire tables tree (a parent and > > relevant children) at the remote side, at least, it shall > > be considered as a unified data chunk from the standpoint of the local side. > > At least for me it's not intuitive to truncate the remote table and its all > dependent tables even though users explicitly specify ONLY for the foreign > table. As far as I read the past discussion, some people was thinking the > same. > > > > > Please assume if file_fdw could map 3 different CSV files, then > > truncate on the foreign table may eliminate just 1 of 3 files. > > Is it an expected / preferable behavior? > > I think that's up to each FDW. That is, IMO the information about whether > ONLY is specified or not for each table should be passed to FDW. Then FDW > itself should determine how to handle that information. > > Anyway, attached is the updated version of the patch. This is still based on > the latest Kazutaka-san's patch. That is, extra list for ONLY is still passed > to FDW. What about committing this version at first? Then we can continue the > discussion and change the behavior later if necessary. > Ok, it's fair enought for me.
I'll try to sort out my thought, then raise a follow-up discussion if necessary. Best regards, -- HeteroDB, Inc / The PG-Strom Project KaiGai Kohei <kai...@heterodb.com>
