File: gdbm.info,  Node: Crash Tolerance,  Next: Options,  Prev: Recovery,  Up: Top

17 Crash Tolerance
******************

Crash tolerance is a new (as of release 1.21) feature that can be
enabled at compile time, and used in environments with appropriate
support from the OS and the filesystem.  As of version 1.24, this means
a Linux kernel 5.12.12 or later and a filesystem that supports reflink
copying, such as XFS, BtrFS, or OCFS2.  If these prerequisites are met,
crash tolerance code will be enabled automatically by the 'configure'
script when building the package.

   The crash-tolerance mechanism, when used correctly, guarantees that a
logically consistent (*note Database consistency::) recent state of
application data can be recovered following a crash.  Specifically, it
guarantees that the state of the database file corresponding to the most
recent successful 'gdbm_sync' call can be recovered.

   If the new mechanism is used correctly, crashes such as power
outages, OS kernel panics, and (some) application process crashes will
be tolerated.  Non-tolerated failures include physical destruction of
storage devices and corruption due to bugs in application logic.  For
example, the new mechanism won't help if a pointer bug in your
application corrupts 'GDBM''s private in-memory data which in turn
corrupts the database file.

   In the following sections we will describe how to enable crash
tolerance in your application and what to do if a crash occurs.

   The design rationale of the crash tolerance mechanism is described in
detail in the article, 'Crashproofing the Original NoSQL Key-Value
Store', by Terence Kelly, 'ACM Queue magazine', July/August 2021,
available from the ACM Digital Library
(https://queue.acm.org/DrillBits5/).  If you have difficulty retrieving
this paper, please contact the author at ,
, or .

* Menu:

* Filesystems supporting crash tolerance::
* Enabling crash tolerance::
* Synchronizing the Database::
* Crash recovery::
* Manual crash recovery::
* Performance Impact::
* Availability::
* Numsync::
* Crash Tolerance API::