Berkeley DB: log_get
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++

# log_get |

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    #include <db.h>

    int
    log_get(DB_ENV *env, DB_LSN *lsn, DBT *data, u_int32_t flags);

# Description

The log_get function 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 DB_ENV handle concurrently, one of the DB_DBT_MALLOC, DB_DBT_REALLOC, or DB_DBT_USERMEM flags must be specified for any DBT used for data retrieval.

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

DB_CHECKPOINT
  The last record written with the DB_CHECKPOINT flag specified to the log_put function is returned in the data argument. The lsn argument is overwritten with the DB_LSN 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 log_get function will return DB_NOTFOUND.

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 DB_LSN of the record returned.

  If the log is empty, the log_get function will return DB_NOTFOUND.

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

  If the log is empty, the log_get function will return DB_NOTFOUND.

DB_NEXT, DB_PREV
  The current log position is advanced to the next (previous) record in the log, and that record is returned in the data argument. The lsn argument is overwritten with the DB_LSN of the record returned.

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

  If the log was opened with the DB_THREAD flag set, calls to log_get with the DB_NEXT (DB_PREV) flag set will return EINVAL.

DB_CURRENT
  Return the log record to which the log currently refers.

  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, log_get will return EINVAL.

DB_SET
  Retrieve the record specified by the lsn argument. If the specified DB_LSN is invalid (for example, it does not appear in the log) log_get will return EINVAL.

Otherwise, the log_get function returns a non-zero error value on failure and 0 on success.

# Errors

The log_get function may fail and return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

  The DB_NEXT or DB_PREV flags were set and the log was opened with the DB_THREAD flag set.

  The DB_CURRENT flag was set and the log pointer had not yet been initialized.

  The DB_SET flag was set and the specified log sequence number does not exist.

The log_get function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the log_get function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

DB_ENV->set_lg_bsize, DB_ENV->set_lg_dir, DB_ENV->set_lg_max, DB_ENV->set_lg_regionmax, log_archive, log_compare, log_file, log_flush, log_get, log_put, log_register, log_stat, and log_unregister.`

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