Berkeley DB: DbLog.get
Полезная информация

DbLog.get


import com.sleepycat.db.*;

public void get(DbLsn lsn, Dbt data, int flags) throws DbException;

Description

The DbLog.get method implements a cursor inside of the log, retrieving records from the log according to the lsn and flags arguments.

The data field of the data structure is set to the record retrieved and the size field indicates the number of bytes in the record. See Dbt for a description of other fields in the data structure. When multiple threads are using the returned log handle concurrently, either the Db.DB_DBT_MALLOC or Db.DB_DBT_USERMEM flags must be specified for any Dbt used for data retrieval.

The flags argument must be set to exactly one of the following values:

Db.DB_CHECKPOINT
The last record written with the DB_CHECKPOINT flag specified to the DbLog.put method is returned in the data argument. The lsn argument is overwritten with the DbLsn of the record returned. If no record has been previously written with the DB_CHECKPOINT flag specified, the first record in the log is returned.

If the log is empty, the DbLog.get method will return DB_NOTFOUND.

Db.DB_FIRST
The first record from any of the log files found in the log directory is returned in the data argument. The lsn argument is overwritten with the DbLsn of the record returned.

If the log is empty, the DbLog.get method will return DB_NOTFOUND.

Db.DB_LAST
The last record in the log is returned in the data argument. The lsn argument is overwritten with the DbLsn of the record returned.

If the log is empty, the DbLog.get method will return DB_NOTFOUND.

Db.DB_NEXT
The current log position is advanced to the next record in the log and that record is returned in the data argument. The lsn argument is overwritten with the DbLsn of the record returned.

If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, DbLog.get will return the first record in the log. If the last log record has already been returned or the log is empty, the DbLog.get method will return DB_NOTFOUND.

If the log was opened with the DB_THREAD flag set, calls to DbLog.get with the DB_NEXT flag set will return EINVAL.

Db.DB_PREV
The current log position is moved to the previous record in the log and that record is returned in the data argument. The lsn argument is overwritten with the DbLsn of the record returned.

If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, DbLog.get will return the last record in the log. If the first log record has already been returned or the log is empty, the DbLog.get method will return DB_NOTFOUND.

If the log was opened with the DB_THREAD flag set, calls to DbLog.get with the DB_PREV flag set will return EINVAL.

Db.DB_CURRENT
Return the log record currently referenced by the log.

If the log pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, or if the log was opened with the DB_THREAD flag set, DbLog.get will return EINVAL.

Db.DB_SET
Retrieve the record specified by the lsn argument. If the specified DbLsn is invalid (e.g., does not appear in the log) DbLog.get will return EINVAL.

Otherwise, the DbLog.get method throws an exception that encapsulates an errno on failure.

Errors

If a fatal error occurs in Berkeley DB, the DbLog.get method may fail and throw a DbRunRecoveryException, at which point all subsequent database calls will also fail in the same way.

The DbLog.get method may fail and throw an exception for any of the errors specified for the following Berkeley DB and C library functions: abort(3), atoi(3), close(3), closedir(3), fcntl(3), fflush(3), fprintf(3), free(3), getenv(3), getpid(3), getuid(3), isdigit(3), lseek(3), malloc(3), memcpy(3), memset(3), open(3), opendir(3), read(3), readdir(3), realloc(3), sigfillset(3), sigprocmask(3), snprintf(3), stat(3), strchr(3), strerror(3), strlen(3), strncmp(3), unlink(3), vfprintf(3), and vsnprintf(3).

In addition, the DbLog.get method may fail and throw an exception encapsulating errno for the following conditions:

EINVAL
An invalid flag value or parameter was specified.

The DB_FIRST flag was specified and no log files were found.

Class

DbLog

See Also

DbLog.archive, DbLog.close, DbLog.compare, DbLog.file, DbLog.flush, DbLog.get, DbLog.open, DbLog.put, DbLog.db_register, DbLog.stat, DbLog.unlink and DbLog.db_unregister.