PostgreSQL version:

max_prepared_transactions

Sets the maximum number of transactions that can be in the prepared state simultaneously (see sql-prepare-transaction). Setting this parameter to zero (which is the default) disables the prepared-transaction feature. This parameter can only be set at server start.

If you are not planning to use prepared transactions, this parameter should be set to zero to prevent accidental creation of prepared transactions. If you are using prepared transactions, you will probably want max_prepared_transactions to be at least as large as max_connections, so that every session can have a prepared transaction pending.

When running a standby server, you must set this parameter to the same or higher value than on the master server. Otherwise, queries will not be allowed in the standby server.

Recommendations

Most applications do not use XA prepared transactions, so should set this parameter to 0. If you do require prepared transactions, you should set this equal to max_connections to avoid blocking. May require increasing kernel memory parameters.

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