SET TRANSACTION

reference

The SET TRANSACTION statement enables you to specify settings for a transaction.

Purpose

The SET TRANSACTION statement enables you to specify settings for an ACID transaction. Refer to SQL++ Support for Couchbase Transactions for further information.

This statement may only be used within a transaction.

If you are using the Query REST API, you must set the txid query parameter to specify the transaction ID.

If you are using the Query Workbench, you don’t need to specify the transaction ID, as long as the statement is part of a multi-statement request. When you start a transaction within a multi-statement request, all statements within the request are assumed to be part of the same transaction until you rollback or commit the transaction.

Similarly, if you are using the cbq shell, you don’t need to specify the transaction ID. Once you have started a transaction, all statements within the cbq shell session are assumed to be part of the same transaction until you rollback or commit the transaction. ^[1]

You may also optionally specify settings when you start the transaction using the BEGIN TRANSACTION command.

Currently, the only available transaction setting is "isolation level read committed". This setting is enabled by default. The SET TRANSACTION statement is therefore optional and may be omitted.

Syntax

set-transaction ::= 'SET' 'TRANSACTION' 'ISOLATION' 'LEVEL' 'READ' 'COMMITTED'

Example

If you want to try this example, first refer to Preparation to set up your environment.

Example 1. Specify transaction settings

Transaction

-- Start the transaction
BEGIN WORK;

-- Specify transaction settings
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

-- Create a booking document
UPSERT INTO bookings
VALUES("bf7ad6fa-bdb9-4099-a840-196e47179f03", {
  "date": "07/24/2021",
  "flight": "WN533",
  "flighttime": 7713,
  "price": 964.13,
  "route": "63986"
});

-- Set a savepoint
SAVEPOINT s1;

-- Update the booking document to include a user
UPDATE bookings AS b
SET b.`user` = "0"
WHERE META(b).id = "bf7ad6fa-bdb9-4099-a840-196e47179f03";

-- Check the content of the booking and user
SELECT b.*, u.name
FROM bookings b
JOIN users u
ON b.`user` = META(u).id
WHERE META(b).id = "bf7ad6fa-bdb9-4099-a840-196e47179f03";

-- Set a second savepoint
SAVEPOINT s2;

-- Update the booking documents to change the user
UPDATE bookings AS b
SET b.`user` = "1"
WHERE META(b).id = "bf7ad6fa-bdb9-4099-a840-196e47179f03";

-- Check the content of the booking and user
SELECT b.*, u.name
FROM bookings b
JOIN users u
ON b.`user` = META(u).id
WHERE META(b).id = "bf7ad6fa-bdb9-4099-a840-196e47179f03";

-- Roll back the transaction to the second savepoint
ROLLBACK TRAN TO SAVEPOINT s2;

-- Check the content of the booking and user again
SELECT b.*, u.name
FROM bookings b
JOIN users u
ON b.`user` = META(u).id
WHERE META(b).id = "bf7ad6fa-bdb9-4099-a840-196e47179f03";

-- Commit the transaction
COMMIT WORK;

Results

[
  {
    "_sequence_num": 1,
    "_sequence_query": "-- Start the transaction\nBEGIN WORK;",
    "_sequence_query_status": "success",
    "_sequence_result": [
      {
        "txid": "d81d9b4a-b758-4f98-b007-87ba262d3a51" (1)
      }
    ]
  },
  {
    "_sequence_num": 2,
    "_sequence_query": "\n\n-- Specify transaction settings\nSET TRANSACTION ISOLATION LEVEL READ COMMITTED;",
    "_sequence_query_status": "success",
    "_sequence_result": {
      "results": []
    }
  },
  {
    "_sequence_num": 3,
    "_sequence_query": "\n\n-- Create a booking document\nUPSERT INTO `travel-sample`.tenant_agent_00.bookings\nVALUES(\"bf7ad6fa-bdb9-4099-a840-196e47179f03\", {\n  \"date\": \"07/24/2021\",\n  \"flight\": \"WN533\",\n  \"flighttime\": 7713,\n  \"price\": 964.13,\n  \"route\": \"63986\"\n});",
    "_sequence_query_status": "success",
    "_sequence_result": {
      "results": []
    }
  },
// ...

1	Beginning a transaction returns a transaction ID.

For an overview of Couchbase transactions, refer to Transactions.
To begin a transaction, refer to BEGIN TRANSACTION.
To set a savepoint, refer to SAVEPOINT.
To rollback a transaction, refer to ROLLBACK TRANSACTION.
To commit a transaction, refer to COMMIT TRANSACTION.
Blog post: Couchbase Transactions: Elastic, Scalable, and Distributed.

1. You must be using cbq shell version 2.0 or above to use the automatic transaction ID functionality.

SET TRANSACTION

Purpose

Syntax

Example

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