1 <?xml version="1.0" encoding="utf-8"?>

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

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

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

    14 This document talks about the situations where data corruption or database

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

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

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

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

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

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

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

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

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

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

    25 by recovering the database.</p>

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

    27 loss.</p>

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

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

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

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

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

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

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

    35 </conbody></concept>