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ivm-extension

Incrementally maintain view result using query PRAGMA ivm_upsert('catalog', 'schema', 'result');

Read more here

Usage

Given a base table hello and a view result on top of hello, this extension incrementally computes the changes to the view result when the underlying table hello changes.

This extension assumes that changes to base table hello are present in delta table delta_hello. This table additionally has a multiplicity column _duckdb_ivm_multiplicity of type BOOL. duckdb_ivm_multiplicity=true means insertions and duckdb_ivm_multiplicity means deletion. Updates to a row in base table hello are modelled as deletion+insertion.

First create the base table and the view:

CREATE TABLE hello(a INTEGER, b INTEGER , c VARCHAR);
CREATE VIEW result AS (SELECT sum(a), count(c), b FROM hello GROUP BY b);

Create delta_hello:

CREATE TABLE delta_hello AS (SELECT * FROM hello LIMIT 0);
ALTER TABLE delta_hello ADD COLUMN _duckdb_ivm_multiplicity BOOL;
INSERT INTO delta_hello VALUES (1,1, 'Mark',true), (2,2, 'Hannes',false), (3,1, 'Kriti',true), (4,1, 'Peter',false);

NOTE: The extension assumes the presence of the delta base table delta_hello.

Incrementally maintaining view result

Run the extension as

PRAGMA ivm_upsert('memory', 'main','result');

The output of the above will be the table delta_result, which will contain incremental processing of the changes to the base table of view result.

Extent of SQL Support

  • Only SELECT, FILTER, GROUP BY, PROJECTION
  • Aggregations supported: SUM, COUNT
  • Joins, nested-subqueries and other SQL clauses like HAVING not supported.

Known issues

IVM on queries in which the base table returns no data because of a WHERE clause, will fail. So, while using WHERE, always ensure that the base table returns a non-empty result. More details in this issue.

Building the Extension

  • Download the files in the repo into folder duckdb_project_root/extension/ivm
  • Search for JSON_EXTENSION and make similar changes for IVM_EXTENSION
  • Build the duckdb binary using make. The IVM extension will be included in the binary
  • Enable debug mode in extension using make debug

Running Tests

  • The tests are present in project_root/tests.
  • Create a folder duckdb_project_root/test/ivm.
  • Copy the test files into the above folder.
  • Use the unittest executable and provide name of the test as program argument