PropertyValue

Command-Line Format

--transaction-read-only[={OFF|ON}]

System Variable (>= 5.7.20)

Scope (>= 5.7.20)

Global, Session

Dynamic (>= 5.7.20)

Yes

Type

Boolean

Default Value

OFF

The transaction access mode. The value can be OFF (read/write; the default) or ON (read only).

The transaction access mode has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard access-mode assignment semantics, as described later.

To set the global transaction access mode at startup, use the --transaction-read-only server option.

At runtime, the access mode can be set directly using the SET statement to assign a value to the transaction_read_only system variable, or indirectly using the SET TRANSACTION statement. For example, use this SET statement to set the global value:

SET GLOBAL transaction_read_only = ON;

Setting the global transaction_read_only value sets the access mode for all subsequent sessions. Existing sessions are unaffected.

To set the session or next-level transaction_read_only value, use the SET statement. For most session system variables, these statements are equivalent ways to set the value:

SET @@SESSION.var_name = value;

SET SESSION var_name = value;

SET var_name = value;

SET @@var_name = value;

As mentioned previously, the transaction access mode has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set, SET syntax for assigning session system variable values has nonstandard semantics for transaction_read_only,

To set the session access mode, use any of these syntaxes:

SET @@SESSION.transaction_read_only = value;

SET SESSION transaction_read_only = value;

SET transaction_read_only = value;

For each of those syntaxes, these semantics apply:

Sets the access mode for all subsequent transactions performed within the session.

Permitted within transactions, but does not affect the current ongoing transaction.

If executed between transactions, overrides any preceding statement that sets the next-transaction access mode.

To set the next-transaction access mode, use this syntax:

SET @@transaction_read_only = value;

For that syntax, these semantics apply:

Sets the access mode only for the next single transaction performed within the session.

Subsequent transactions revert to the session access mode.

Not permitted within transactions.

Corresponds to SET TRANSACTION {READ WRITE | READ ONLY} (without the SESSION keyword).

Note

transaction_read_only was added in MySQL 5.7.20 as an alias for tx_read_only, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to use transaction_read_only in preference to tx_read_only.