Logging subsystem

This subsystem is used when recovery from application or system failure is necessary.

The log is stored in one or more files in the environment directory. Each file is named using the format log.NNNNNNNNNN, where NNNNNNNNNN is the sequence number of the file within the log.

If the log region is being created and log files are already present, the log files are reviewed and subsequent log writes are appended to the end of the log, rather than overwriting current log entries.

The lock subsystem is created, initialized, and opened by calls to BDB::Env#open with the BDB::INIT_LOG flag specified.

The following options can be given when the environnement is created

"set_lg_bsize"

Set log buffer size

"set_lg_dir"

Set the environment logging directory

"set_lg_max"

Set log file size

BDB::Env

Methods

log_archive(flags = 0)

The log_archive function return an array of log or database file names.

flags value must be set to 0 or the value BDB::ARCH_DATA

((|BDB::ARCH_DATA|)), ((|BDB::ARCH_LOG|))

log_checkpoint(string)

same as log_put(string, BDB::CHECKPOINT)

log_curlsn(string)

same as log_put(string, BDB::CURLSN)

log_each { |string, lsn| ... }

Implement an iterator inside of the log

log_flush([string])

same as log_put(string, BDB::FLUSH)

Without argument, garantee that all records are written to the disk

log_get(flag)

The log_get return an array [String, BDB::Lsn] according to the flag value.

flag can has the value BDB::CHECKPOINT, BDB::FIRST, BDB::LAST, BDB::NEXT, BDB::PREV, BDB::CURRENT

log_put(string, flag = 0)

The log_put function appends records to the log. It return an object BDB::Lsn

flag can have the value BDB::CHECKPOINT, BDB::CURLSN, BDB::FLUSH

log_reverse_each { |string, lsn| ... }

Implement an iterator inside of the log

log_stat

return log statistics

BDB::Common

Methods

log_register(name)

The log_register function registers a file name.

log_unregister()

The log_unregister function unregisters a file name.

BDB::Lsn

include Comparable

<=>

compare 2 BDB::Lsn

log_file(name)

file(name)

The log_file function maps BDB::Lsn structures to file names

log_flush

flush

The log_flush function guarantees that all log records whose DBB:Lsn are less than or equal to the current lsn have been written to disk.

log_get

get

return the String associated with this BDB::Lsn