mco_edge_clear

Removes completed transactions from the edge database ring buffer to free up space.

For an overview, see the Edge Client page.

Prototype

    MCO_RET mco_edge_clear(mco_edge_h con, unsigned int clear_flags);
    

Arguments

Description

Removes completed transactions from the local ring buffer, freeing space for new data. This function is essential for maintaining the continuous operation of the edge database, as the ring buffer has a fixed size.

The behavior of the clearing process is controlled by the clear_flags parameter, which can be a combination of the following flags:

• MCO_EDGE_CLEAR_ACK (0x01): Removes only transactions that have been successfully sent to the server and acknowledged (ACK). This is the safest mode, guaranteeing no data loss.
• MCO_EDGE_CLEAR_SENT (0x02): Removes transactions that have been sent to the server but not yet acknowledged. Use with caution, as data loss is possible if the server fails before acknowledging.
• MCO_EDGE_CLEAR_ALL (0x04): Removes all completed transactions, regardless of their synchronization status. This may result in significant data loss and should only be used in specific recovery scenarios.
• MCO_EDGE_SINGLE_TRANSACTION (0x100): Limits the operation to removing at most one transaction per call. Useful for fine-grained buffer management.

Clear Callback: If a clear_callback was specified in the mco_edge_params_t structure during database initialization, mco_edge_clear() will invoke this callback for each object being removed. This allows the application to perform custom cleanup or logging operations.

The callback function prototype is:

    typedef MCO_RET (*mco_edge_clear_callback_t)(
        MCO_Ef *obj,
        mco_uint2 class_code,
        unsigned int clear_flags,
        void *context
    );

Where:

• obj: Handle of the object being removed. It can be used with generated Class_get() wrappers to access field values before the object is destroyed.
• class_code: Internal identifier of the object's class.
• clear_flags: Indicates the state of the transaction to which the object belongs:
  • MCO_EDGE_CLEAR_ACK: Transaction was sent and acknowledged (no data loss).
  • MCO_EDGE_CLEAR_SENT: Transaction was sent but not acknowledged (data loss is possible).
  • MCO_EDGE_CLEAR_ALL: Transaction was not sent (data loss is guaranteed).
• context: User-defined context pointer provided during callback registration.

To mark the end of a transaction, the callback is also invoked with a null object handle:

    (*clear_callback)(0, 0, clear_flags | MCO_EDGE_CLEAR_TRANSACTION_END, context);

The MCO_EDGE_CLEAR_TRANSACTION_END (0x200) flag indicates that all objects for the current transaction have been processed.

Return Codes

Files