Insert Idempotency

Since Timeplus Enterprise v2.4 there are new settings idempotent_id and enable_idempotent_processing:

• INSERT INTO .. SETTINGS idempotent_id='..' VALUES ..
• 选择... FROM .. SETTINGS enable_idempotent_processing=true

These settings allow you to define a unique ID for each batch INSERT. Sending the data with the same value of idempotent_id won't result in duplicated data in the target stream. You can retry safely with those settings.

Here is an example.

Create a stream for testing

Let's create a stream with 2 columns:

CREATE STREAM test_stream(`i` int,  `v` string)

This is an append-only stream. You can insert duplicated data, e.g.

INSERT INTO test43_stream (i, v) VALUES (1, 'a') (1, 'a')

Insert with idempotent_id

Recreate the stream if you have inserted any data. You can run the following SQL multiple times:

INSERT INTO test_stream (i, v) SETTINGS idempotent_id = 'batch1' VALUES (1, 'a') (2, 'b');

Then run

SELECT count() FROM table(test_stream)

You will get 2.

If you remove SETTINGS idempotent_id = 'batch1' and run the SQL again, duplicated data will be inserted.

Streaming SQL with enable_idempotent_processing

When you insert data with idempotent_id, querying the stream with table function will retrieve the historical data of the stream, without duplication. However if you run:

SELECT count() FROM test_stream

Every time you run the INSERT SQL, no matter with idempotent_id or not, a bigger count number will be returned. To enable idempotent processing, set the flag to true in the Streaming SQL, e.g.

SELECT count() FROM test_stream SETTINGS enable_idempotent_processing=true;

With this setting, your Streaming SQL will only emit results when it accepts new data.