# mco_HA_set_trans_window_size

This function is called by the master to set the transaction packet size.

### For an overview see page HA Applications

### Prototype

        MCO_RET	mco_HA_set_trans_window_size(	mco_trans_h  t,
                             uint4 window_size)

### Arguments

t | Transaction handle for an active `READ_WRITE` transaction.
window_size | Transaction window (packet) size (default is 1).

### Description

This function is called by the master to set the transaction packet size. With synchronous replication (default mode), a replica does not confirm each of the master’s transactions, but a transaction packet as a whole. Thus, the larger the `window_size`, the fewer confirmations the replica will send to the master. This can improve the speed of replication, but the replica can “lag” behind the master up to `window_size` transactions.

It should be called from within the context of an active `READ_WRITE` transaction. Note: With asynchronous replication this function has no effect.

### Return Codes

MCO_S_OK | The master transaction window size was set successfully.
MCO_E_ACCESS | The function was called in a Read-Only transaction context
MCO_E_NOMEM | Out of memory attempting to set up the transaction log.