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<concept id="GUID-898FF7CE-969C-5FE1-9346-34BCBE637A57" xml:lang="en"><title>Data

safety and recovery</title><shortdesc>Databases are very robust and will survive crashes in most situations.

This document talks about the situations where data corruption or database

integrity could be compromised.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>A robust stream structure is used to manage row data within a database.

A database can rely on the permanent file store's update integrity and that

the database will survive a crash in most situations. This excludes the case

where the file itself is corrupted. Such an aborted access causes a rollback

on the database when it is next opened, all committed data is immediately

available, though indexes may have been damaged as for a controlled rollback.</p>

<p>The database reports damage if it considers that it may have damaged indexes.

When this is the case the database can still be used, but attempting to use

any damaged index results in an error. Damaged indexes can be fully restored

by recovering the database.</p>

<p>Compacting the store which contains the database also guarantees no data

loss.</p>

<p>The store used by the database must not be committed or reverted while

the database is inside a transaction. This can lead to loss of structural

integrity within the database. Such damage is not repairable by DBMS. </p>

<p>The database streams cannot be corrupted by any action of DBMS itself,

but misuse of the store, the file or damage to the file system resulting in

such corruption may be detected by the database and reported as an error.

DBMS cannot repair such damage to a database.</p>