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Berkeley DB: log_get
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.
Copyright Sleepycat Software
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