> As I understand it, the current patch performs immediate IVM using AFTER > STATEMENT trigger transition tables. > > However, multiple tables can be modified *before* AFTER STATEMENT triggers > are fired. > > CREATE TABLE example1 (a int); > CREATE TABLE example2 (a int); > > CREATE INCREMENTAL MATERIALIZED VIEW mv AS > SELECT example1.a, example2.a > FROM example1 JOIN example2 ON a; > > WITH > insert1 AS (INSERT INTO example1 VALUES (1)), > insert2 AS (INSERT INTO example2 VALUES (1)) > SELECT NULL; > > Changes to example1 are visible in an AFTER STATEMENT trigger on example2, > and vice versa. Would this not result in the (1, 1) tuple being > "double-counted"? > > IVM needs to either: > > (1) Evaluate deltas "serially' (e.g. EACH ROW triggers) > > (2) Have simultaneous access to multiple deltas: > delta_mv = example1 x delta_example2 + example2 x delta_example1 - > delta_example1 x delta_example2 > > This latter method is the "logged" approach that has been discussed for > deferred evaluation. > > tl;dr It seems that AFTER STATEMENT triggers required a deferred-like > implementation anyway.
You are right, the latest patch doesn't support the situation where multiple tables are modified in a query. I noticed this when working on self-join, which also virtually need to handle multiple table modification.
I am now working on this issue and the next patch will enable to handle this situation. I plan to submit the patch during this month. Roughly speaking, in the new implementation, AFTER STATEMENT triggers are used to collect information of modified table and its changes (= transition tables), and then the only last trigger updates the view. This will avoid the double-counting. I think this implementation also would be a base of deferred approach implementation in future where "logs" are used instead of transition tables.