Error handling

WiredTiger operations return a value of 0 on success and a non-zero value on error. Error codes may be either positive or negative: positive error codes are standard error codes as described for POSIX-like systems (for example, EINVAL or EBUSY), negative error codes are WiredTiger-specific (for example, WT_ROLLBACK).

WiredTiger-specific error codes always appear in the -31,800 to -31,999 range.

The following is a list of possible WiredTiger-specific errors:

WT_ROLLBACK

This error is generated when an operation cannot be completed due to a conflict with concurrent operations. The operation may be retried; if a transaction is in progress, it should be rolled back and the operation retried in a new transaction.

WT_DUPLICATE_KEY

This error is generated when the application attempts to insert a record with the same key as an existing record without the 'overwrite' configuration to WT_SESSION::open_cursor.

WT_ERROR

This error is returned when an error is not covered by a specific error return.

WT_NOTFOUND

This error indicates an operation did not find a value to return. This includes cursor search and other operations where no record matched the cursor's search key such as WT_CURSOR::update or WT_CURSOR::remove.

WT_PANIC

This error indicates an underlying problem that requires the application exit and restart. The application can exit immediately when WT_PANIC is returned from a WiredTiger interface, no further WiredTiger calls are required.

WT_RUN_RECOVERY

This error is generated when wiredtiger_open is configured to return an error if recovery is required to use the database.

Translating errors

The WT_SESSION::strerror and wiredtiger_strerror functions return the standard text message associated with any WiredTiger, ISO C, or POSIX standard API.

        const char *key = "non-existent key";
        cursor->set_key(cursor, key);
        if ((ret = cursor->remove(cursor)) != 0) {
                fprintf(stderr,
                    "cursor.remove: %s\n",
                    cursor->session->strerror(cursor->session, ret));
                return (ret);
        }

        const char *key = "non-existent key";
        cursor->set_key(cursor, key);
        if ((ret = cursor->remove(cursor)) != 0) {
                fprintf(stderr,
                    "cursor.remove: %s\n", wiredtiger_strerror(ret));
                return (ret);
        }

Note that wiredtiger_strerror is not thread-safe.

Error handling using the WT_EVENT_HANDLER

More complex error handling can be configured by passing an implementation of WT_EVENT_HANDLER to wiredtiger_open or WT_CONNECTION::open_session.

For example, both informational and error messages might be passed to an application-specific logging function that added a timestamp and logged the message to a file, and error messages might additionally be output to the stderr file stream.

/*
 * Create our own event handler structure to allow us to pass context through
 * to event handler callbacks. For this to work the WiredTiger event handler
 * must appear first in our custom event handler structure.
 */
typedef struct {
        WT_EVENT_HANDLER h;
        const char *app_id;
} CUSTOM_EVENT_HANDLER;

/*
 * handle_wiredtiger_error --
 *      Function to handle error callbacks from WiredTiger.
 */
int
handle_wiredtiger_error(WT_EVENT_HANDLER *handler,
    WT_SESSION *session, int error, const char *message)
{
        CUSTOM_EVENT_HANDLER *custom_handler;

        /* Cast the handler back to our custom handler. */
        custom_handler = (CUSTOM_EVENT_HANDLER *)handler;

        /* Report the error on the console. */
        fprintf(stderr,
            "app_id %s, thread context %p, error %d, message %s\n",
            custom_handler->app_id, session, error, message);

        return (0);
}

/*
 * handle_wiredtiger_message --
 *      Function to handle message callbacks from WiredTiger.
 */
int
handle_wiredtiger_message(
    WT_EVENT_HANDLER *handler, WT_SESSION *session, const char *message)
{
        /* Cast the handler back to our custom handler. */
        printf("app id %s, thread context %p, message %s\n",
            ((CUSTOM_EVENT_HANDLER *)handler)->app_id, session, message);

        return (0);
}

        CUSTOM_EVENT_HANDLER event_handler;

        event_handler.h.handle_error = handle_wiredtiger_error;
        event_handler.h.handle_message = handle_wiredtiger_message;
        /* Set handlers to NULL to use the default handler. */
        event_handler.h.handle_progress = NULL;
        event_handler.h.handle_close = NULL;
        event_handler.app_id = "example_event_handler";

        ret = wiredtiger_open(home,
            (WT_EVENT_HANDLER *)&event_handler, "create", &conn);