foedus::savepoint Namespace Reference

Savepoint Manager, which durably and atomically remembers what happened in the engine occasionally (eg. More...

Detailed Description

Savepoint Manager, which durably and atomically remembers what happened in the engine occasionally (eg.

every group commit).

Overview

In nutshell, this package durably and atomically (*) writes out a tiny file (savepoint file) whenever we advance the global epoch, replacing the savepoint file durably and atomically. The savepoint file is an XML file that describes the progress of individual loggers, log gleaners, and whatever we have to take note for durability and serializablity. These are very compact data, essentially only one or two integers per modules/threads. Thus, the dominating cost is fsync(), which is not cheap but we are okay to pay assuming epoch-based commit and reasonably fast media (SSD/NVRAM).

Why XML

As writing savepoint files happens only occasionally, file format doesn't matter for performance. Thus, we use XML for better debuggability and flexibility. We already use tinyxml for config files, so why not.

Terminology

We named this package savepoint rather than checkpoint. Checkpoint has a slightly different meaning in DBMS, so we avoid that. Savepoint also has a different meaning in DBMS, but it's very different, so no confusion.

See also

foedus::fs::durable_atomic_rename()

Classes
struct	FixedSavepoint
	Savepoint that can be stored in shared memory. More...
struct	LoggerSavepointInfo
	Information in savepoint for one logger. More...
struct	Savepoint
	The information we maintain in savepoint manager and externalize to a file. More...
class	SavepointManager
	Savepoint manager that atomically and durably writes out a savepoint file. More...
struct	SavepointManagerControlBlock
	Shared data in SavepointManagerPimpl. More...
class	SavepointManagerPimpl
	Pimpl object of SavepointManager. More...
struct	SavepointOptions
	Set of options for savepoint manager. More...

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Class Documentation

struct foedus::savepoint::LoggerSavepointInfo

Information in savepoint for one logger.

Definition at line 140 of file savepoint.hpp.

Class Members
LogFileOrdinal	current_log_file_	Indicates the log file each logger is currently appending to.
uint64_t	current_log_file_offset_durable_	Indicates the exclusive end of durable region in the current log file. In other words, epochs are larger than durable_epoch_ from this offset. During restart, current log files are truncated to this size to discard incomplete logs.
LogFileOrdinal	oldest_log_file_	Ordinal of the oldest active log file in each logger. Invariant oldest_log_files_[x] <= current_log_files_[x] Each logger writes out files suffixed with ordinal (eg ".0", ".1"...). The older logs files are deactivated and deleted after log gleaner consumes them. This variable indicates the oldest active file for each logger.
uint64_t	oldest_log_file_offset_begin_	Indicates the inclusive beginning of active region in the oldest log file.