Transactions

Introduction to Redshift

Jason Myers

Principal Engineer

Motivation for using transactions

SELECT name,
       priority,
  FROM data_log
       -- SYSDATE = 2024-02-07 00:17:24.259227
 WHERE intake_ts < SYSDATE;

SELECT name,
       data_size,
  FROM data_details
       -- SYSDATE = 2024-02-07 00:18:04.830527
 WHERE current_intake_date < SYSDATE;

Statement grouping example

data_intake

name	priority
idaho_monitoring_locations	1
idaho_samples	2
idaho_site_id	3

UPDATE data_intake 
   SET priority=1 
 WHERE name='idaho_samples';

UPDATE data_intake 
   SET priority=2 
 WHERE name='idaho_monitoring_locations';

Errored table results

data_intake

name	priority
idaho_monitoring_locations	1
idaho_samples	1
idaho_site_id	3

Transaction advantages and considerations

Consistent data outcomes
Requiring success or failure for a group of queries
Concurrent operations

Default Execution Behavior

Each SQL statement is a transaction!

Transactions Affect some Functions

Set at start of transactions and stay the same
- SYSDATE, TIMESTAMP, CURRENT_DATE

Some functions skirt around Transactions

Set at each statement execution
- GETDATE, TIMEOFDAY

Transactions Structure

Opens with BEGIN; or START TRANSACTION;
Contains one or more SQL statements with a semicolon after each one
Closes with END; or COMMIT;
NOTE: Semicolons matter

BEGIN;

  query1;
  query2;

END;

Getting consistent query results

-- Start a transaction
BEGIN;
SELECT name,
       priority,
  FROM data_log
       -- SYSDATE = 2024-02-07 00:17:24.259227
 WHERE intake_ts < SYSDATE;

SELECT name,
       data_size,
  FROM data_details
       -- SYSDATE = 2024-02-07 00:17:24.259227
 WHERE current_intake_date < SYSDATE;
-- End a transaction
END;

Function behavior in transactions

-- Start a transaction
BEGIN;
SELECT name,
       priority,
  FROM data_intake
       -- GETDATE = 2024-02-07 00:17:24.259227
 WHERE data_intake_ts < GETDATE();

 SELECT name,
       data_size,
  FROM data_details
       -- GETDATE = 2024-02-07 00:18:44.830527
 WHERE current_intake_date < GETDATE();
-- End a transaction
END;

Let's practice!

Introduction to Redshift