Re: Implementing Incremental View Maintenance
От | Yugo NAGATA |
---|---|
Тема | Re: Implementing Incremental View Maintenance |
Дата | |
Msg-id | 20200117172118.8ed98492065028da58bc85b2@sraoss.co.jp обсуждение исходный текст |
Ответ на | Re: Implementing Incremental View Maintenance (nuko yokohama <nuko.yokohama@gmail.com>) |
Список | pgsql-hackers |
On Thu, 16 Jan 2020 18:50:40 +0900 nuko yokohama <nuko.yokohama@gmail.com> wrote: > Error occurs when updating user-defined type columns. > > Create an INCREMENTAL MATERIALIZED VIEW by specifying a query that includes > user-defined type columns. > After the view is created, an error occurs when inserting into the view > source table (including the user-defined type column). > ``` > ERROR: operator does not exist Thank you for your reporting. I think this error occurs because pg_catalog.= is used also for user-defined types. I will fix this. Regards, Yugo Nagata > ``` > > An execution example is shown below. > > ``` > [ec2-user@ip-10-0-1-10 ivm]$ psql testdb -a -f extension-insert.sql > -- > -- pg_fraction: https://github.com/nuko-yokohama/pg_fraction > -- > DROP EXTENSION IF EXISTS pg_fraction CASCADE; > psql:extension-insert.sql:4: NOTICE: drop cascades to column data of table > foo > DROP EXTENSION > DROP TABLE IF EXISTS foo CASCADE; > DROP TABLE > CREATE EXTENSION IF NOT EXISTS pg_fraction; > CREATE EXTENSION > \dx > List of installed extensions > Name | Version | Schema | Description > -------------+---------+------------+------------------------------ > pg_fraction | 1.0 | public | fraction data type > plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language > (2 rows) > > \dT+ fraction > List of data types > Schema | Name | Internal name | Size | Elements | Owner | Access > privileges | Description > --------+----------+---------------+------+----------+----------+-------------------+------------- > public | fraction | fraction | 16 | | postgres | > | > (1 row) > > CREATE TABLE foo (id int, data fraction); > CREATE TABLE > INSERT INTO foo (id, data) VALUES (1,'2/3'),(2,'1/3'),(3,'1/2'); > INSERT 0 3 > SELECT id, data FROM foo WHERE data >= '1/2'; > id | data > ----+------ > 1 | 2/3 > 3 | 1/2 > (2 rows) > > CREATE INCREMENTAL MATERIALIZED VIEW foo_imv AS SELECT id, data FROM foo > WHERE data >= '1/2'; > SELECT 2 > TABLE foo_imv; > id | data > ----+------ > 1 | 2/3 > 3 | 1/2 > (2 rows) > > INSERT INTO foo (id, data) VALUES (4,'2/3'),(5,'2/5'),(6,'3/6'); -- error > psql:extension-insert.sql:17: ERROR: operator does not exist: fraction > pg_catalog.= fraction > LINE 1: ...(mv.id IS NULL AND diff.id IS NULL)) AND (mv.data OPERATOR(p... > ^ > HINT: No operator matches the given name and argument types. You might > need to add explicit type casts. > QUERY: WITH updt AS (UPDATE public.foo_imv AS mv SET __ivm_count__ = > mv.__ivm_count__ OPERATOR(pg_catalog.+) diff.__ivm_count__ FROM > pg_temp_3.pg_temp_73900 AS diff WHERE (mv.id OPERATOR(pg_catalog.=) diff.id > OR (mv.id IS NULL AND diff.id IS NULL)) AND (mv.data OPERATOR(pg_catalog.=) > diff.data OR (mv.data IS NULL AND diff.data IS NULL)) RETURNING mv.id, > mv.data) INSERT INTO public.foo_imv SELECT * FROM pg_temp_3.pg_temp_73900 > AS diff WHERE NOT EXISTS (SELECT 1 FROM updt AS mv WHERE (mv.id > OPERATOR(pg_catalog.=) diff.id OR (mv.id IS NULL AND diff.id IS NULL)) AND > (mv.data OPERATOR(pg_catalog.=) diff.data OR (mv.data IS NULL AND diff.data > IS NULL))); > TABLE foo; > id | data > ----+------ > 1 | 2/3 > 2 | 1/3 > 3 | 1/2 > (3 rows) > > TABLE foo_imv; > id | data > ----+------ > 1 | 2/3 > 3 | 1/2 > (2 rows) > > DROP MATERIALIZED VIEW foo_imv; > DROP MATERIALIZED VIEW > INSERT INTO foo (id, data) VALUES (4,'2/3'),(5,'2/5'),(6,'3/6'); > INSERT 0 3 > TABLE foo; > id | data > ----+------ > 1 | 2/3 > 2 | 1/3 > 3 | 1/2 > 4 | 2/3 > 5 | 2/5 > 6 | 1/2 > (6 rows) > > ``` > > Best regards. > > 2018年12月27日(木) 21:57 Yugo Nagata <nagata@sraoss.co.jp>: > > > Hi, > > > > I would like to implement Incremental View Maintenance (IVM) on > > PostgreSQL. > > IVM is a technique to maintain materialized views which computes and > > applies > > only the incremental changes to the materialized views rather than > > recomputate the contents as the current REFRESH command does. > > > > I had a presentation on our PoC implementation of IVM at PGConf.eu 2018 > > [1]. > > Our implementation uses row OIDs to compute deltas for materialized > > views. > > The basic idea is that if we have information about which rows in base > > tables > > are contributing to generate a certain row in a matview then we can > > identify > > the affected rows when a base table is updated. This is based on an idea of > > Dr. Masunaga [2] who is a member of our group and inspired from ID-based > > approach[3]. > > > > In our implementation, the mapping of the row OIDs of the materialized view > > and the base tables are stored in "OID map". When a base relation is > > modified, > > AFTER trigger is executed and the delta is recorded in delta tables using > > the transition table feature. The accual udpate of the matview is triggerd > > by REFRESH command with INCREMENTALLY option. > > > > However, we realize problems of our implementation. First, WITH OIDS will > > be removed since PG12, so OIDs are no longer available. Besides this, it > > would > > be hard to implement this since it needs many changes of executor nodes to > > collect base tables's OIDs during execuing a query. Also, the cost of > > maintaining > > OID map would be high. > > > > For these reasons, we started to think to implement IVM without relying on > > OIDs > > and made a bit more surveys. > > > > We also looked at Kevin Grittner's discussion [4] on incremental matview > > maintenance. In this discussion, Kevin proposed to use counting algorithm > > [5] > > to handle projection views (using DISTNICT) properly. This algorithm need > > an > > additional system column, count_t, in materialized views and delta tables > > of > > base tables. > > > > However, the discussion about IVM is now stoped, so we would like to > > restart and > > progress this. > > > > > > Through our PoC inplementation and surveys, I think we need to think at > > least > > the followings for implementing IVM. > > > > 1. How to extract changes on base tables > > > > I think there would be at least two approaches for it. > > > > - Using transition table in AFTER triggers > > - Extracting changes from WAL using logical decoding > > > > In our PoC implementation, we used AFTER trigger and transition tables, > > but using > > logical decoding might be better from the point of performance of base > > table > > modification. > > > > If we can represent a change of UPDATE on a base table as query-like > > rather than > > OLD and NEW, it may be possible to update the materialized view directly > > instead > > of performing delete & insert. > > > > > > 2. How to compute the delta to be applied to materialized views > > > > Essentially, IVM is based on relational algebra. Theorically, changes on > > base > > tables are represented as deltas on this, like "R <- R + dR", and the > > delta on > > the materialized view is computed using base table deltas based on "change > > propagation equations". For implementation, we have to derive the > > equation from > > the view definition query (Query tree, or Plan tree?) and describe this as > > SQL > > query to compulte delta to be applied to the materialized view. > > > > There could be several operations for view definition: selection, > > projection, > > join, aggregation, union, difference, intersection, etc. If we can > > prepare a > > module for each operation, it makes IVM extensable, so we can start a > > simple > > view definition, and then support more complex views. > > > > > > 3. How to identify rows to be modifed in materialized views > > > > When applying the delta to the materialized view, we have to identify > > which row > > in the matview is corresponding to a row in the delta. A naive method is > > matching > > by using all columns in a tuple, but clearly this is unefficient. If > > thematerialized > > view has unique index, we can use this. Maybe, we have to force > > materialized views > > to have all primary key colums in their base tables. In our PoC > > implementation, we > > used OID to identify rows, but this will be no longer available as said > > above. > > > > > > 4. When to maintain materialized views > > > > There are two candidates of the timing of maintenance, immediate (eager) > > or deferred. > > > > In eager maintenance, the materialized view is updated in the same > > transaction > > where the base table is updated. In deferred maintenance, this is done > > after the > > transaction is commited, for example, when view is accessed, as a response > > to user > > request, etc. > > > > In the previous discussion[4], it is planned to start from "eager" > > approach. In our PoC > > implementaion, we used the other aproach, that is, using REFRESH command > > to perform IVM. > > I am not sure which is better as a start point, but I begin to think that > > the eager > > approach may be more simple since we don't have to maintain base table > > changes in other > > past transactions. > > > > In the eager maintenance approache, we have to consider a race condition > > where two > > different transactions change base tables simultaneously as discussed in > > [4]. > > > > > > [1] > > https://www.postgresql.eu/events/pgconfeu2018/schedule/session/2195-implementing-incremental-view-maintenance-on-postgresql/ > > [2] > > https://ipsj.ixsq.nii.ac.jp/ej/index.php?active_action=repository_view_main_item_detail&page_id=13&block_id=8&item_id=191254&item_no=1 > > (Japanese only) > > [3] https://dl.acm.org/citation.cfm?id=2750546 > > [4] > > https://www.postgresql.org/message-id/flat/1368561126.64093.YahooMailNeo%40web162904.mail.bf1.yahoo.com > > [5] https://dl.acm.org/citation.cfm?id=170066 > > > > Regards, > > -- > > Yugo Nagata <nagata@sraoss.co.jp> > > > > -- Yugo NAGATA <nagata@sraoss.co.jp>
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