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,
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.
typedef struct {
const char *app_id;
} CUSTOM_EVENT_HANDLER;
int
WT_SESSION *session,
int error,
const char *message)
{
CUSTOM_EVENT_HANDLER *custom_handler;
custom_handler = (CUSTOM_EVENT_HANDLER *)handler;
fprintf(stderr,
"app_id %s, thread context %p, error %d, message %s\n",
custom_handler->app_id, session, error, message);
return (0);
}
int
handle_wiredtiger_message(
{
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;
event_handler.h.handle_progress = NULL;
event_handler.h.handle_close = NULL;
event_handler.app_id = "example_event_handler";