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Syntax

FLUSH;

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Purpose of FLUSH

RisingWave uses a snapshot-based mechanism for data durability. Periodically, a snapshot is triggered which flushes operator state to storage like S3. If a failure occurs, operators recover from the latest snapshot. However, snapshots are asynchronous. By default, RisingWave does not guarantee read-after-write consistency — a write may not be visible to subsequent reads immediately. The FLUSH command provides a way to synchronously persist pending changes and ensure subsequent reads reflect the latest data. It blocks until the changes are durable.

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When to use FLUSH

FLUSH should be used after any statements that change data, including:
  • DML like INSERT, UPDATE, or DELETE.
  • DDL creating objects that query the data.
In the example below, FLUSH ensures the pending data changes from the INSERT are persisted, and the new materialized view has been populated before querying it: 
CREATE TABLE users (id INT, name VARCHAR(50));

INSERT INTO users VALUES (1, 'Alice');

FLUSH;

CREATE MATERIALIZED VIEW user_count AS
  SELECT COUNT(*) AS total_users FROM users;

FLUSH;

SELECT * FROM user_count;