Is your MultiValue database Resilient Resilient Mark Fuller

							Is your MultiValue database
Resilient? Mark Fuller, Northgate Information Solutions

People say that ‘the main asset            idle, cost of late billings etc; but
                                           also the non-
                                                                                     (Northgate) stand out from the
                                                                                                        plethora of
of any company is its staff’ and
                                           material             ‘The non-material damages               vendors with
that staff retention is very
                                           damages                                                      resilience
important. I don’t for a minute
                                           that are often       are often very difficult to             features that
disagree, but I would argue that                                quantify.’
                                           very difficult                                               are second to
another asset, that is also vitally
                                           to quantify.                                                 none and
important, is the company’s
                                           Now with the World Wide Web,              ensure that they are the market
data. Data in a database
                                           your systems are visible                  leaders in this field, but all of the
constitutes a substantial
                                           globally and the impact of a              vendors offer some degree of
financial investment, and will
                                           system being down is far more             resilience, some of which is
often contain commercially or
                                           widespread. Worst still in a              ‘free’, so why not implement it?
even socially sensitive
                                           mission critical 24x7 system, it          In keeping with the ‘ease of use’
information. What happens if a
                                           could even mean the difference            of the database, these tend to
company loses its data? What
                                           between life and death!                   be easy to administer and give
can be done to address this
                                                                                     you a viable resilient path when
risk? How does a
                                                                                     coupled with the technologies
MultiValue
database fit into the       ‘Data in a database                                      above. The capabilities of
                            constitutes a                                            MultiValue databases, such as
world of disaster
                                                                                     Reality, mean that you can
recovery? These             substantial financial                                    operate a 24X7 operation, and
are some of the             investment’                                              indeed this has been the case
questions I hope to
                                                                                     for many years in mission
answer below.
                                                                                     critical organisations.
                                            Addressing the
Can you afford                              Risk
not to have a                                                                           Some of the
resilient system?                           Traditionally, these risks have
                                            been managed by simply
                                                                                        solutions
                                            backing up data to magnetic                 available
If a company loses its data then            tape or other storage media,
the penalties could be                      and this should still be a vital
                                            part of any disaster recovery               Most, if not all of the MultiValue
astronomical and are often                                                              vendors provide both
underestimated. Look at some                strategy. However, this is no
                                            longer sufficient on its own for            Transaction Handling and
of the evidence.                                                                        Transaction Logging
                                            most organisations as the cost
                                            of restoring data is prohibitive.           capabilities; lets take a look at
     •    ‘Companies that                   RAID disks and cluster                      what they do.
          aren’t able to resume             technology can also help and
          operations within 10              are in themselves great                     Transaction Handling
          days of a disaster are            technologies, but again, for                provides protection around a
          not likely to survive’            some organisations, these can               series of updates to data files
          (source: Strategic                no longer be relied upon                    from an application by grouping
          Research Institute,               independently, as they only                 the ‘updates’ together. A
          Jan 2002.).                       protect you from approximately              ‘transaction ‘ is a set of related
     •    ‘Problems with IT cost            30% of failures. Another option             database updates that must be
          small and medium                  is to completely outsource the              completed indivisibly for the
          enterprises (SME’s)               hosting of your database to a               database to remain consistent.
          £100 billion in lost              specialised ‘hosting’ company               This effectively means that if
          turnover each year                and pass the risk onto them.                one update fails, they all do and
          according to the                  However, for those                          a ‘roll back’ occurs to ‘remove’
          London Business                   organisations, which wish to                updates and bring the files back
          School. Computer                  maintain their own disaster                 to the state they were in before
          crashes are                       recovery procedures, then a                 the ‘group’ of updates began.
          estimated to cause                MultiValue database is a ‘low               This can protect you from
          losses of £31 million             cost’, efficient database, which            ‘application crashes’ whereby
          each year.’                       addresses these needs.                      some files have been updated
                                                                                        and others haven’t, causing
                                            MultiValue databases have                   downtime while someone
When an incident occurs it is                                                           recovers any inconsistent
                                            been traditionally strong, and
not just the material damages                                                           updates that have broken
                                            secure data stores deployable
that need to be taken into                                                              business logic
                                            at low cost. Some today, such
account, i.e. loss of earnings
                                            as ‘Reality’ from Northgate
while systems are unavailable,
                                            Information Solutions
cost of human resources sitting
                                                                          technologies mentioned above
Transaction Logging                                                       make MultiValue databases a
enhances the data                                                         viable alternative to more
security and resilience of                                                mainstream databases where
a MultiValue database                                                     some of this functionality exists,
by recording all changes                                                  but at far greater costs.
made by both completed
transactions and discrete
updates. This minimises
the loss of valid updates
to your database in the
event of a failure and
enables these updates to
be replayed rapidly to a
restored database.                   systems. Users will connect
                                     and run applications on the
Some vendors now also provide        primary machine and updates
recoverable filing systems           will be seamlessly transferred to
(Rapid Recovery or Journaling        the secondary
filing systems). This effectively    machine and
records all structural changes to    replayed on the
a database. This enables the         database in ‘real-
physical integrity of all files to   time’. If the
be restored within minutes of        primary machine
restarting a database after a        fails the
system failure.                      secondary is
                                     quickly re-
Northgate includes the above         configured as the
options at no extra cost and has     primary and users
further extended the resilience      can then re-
capabilities, which are              connect and
discussed below.                     continue working.
                                     Service is thereby
Shadow Database enhances             maintained with minimal
resilience by allowing two           interruption.
copies of a database to be
                                                Heartbeat is the
                                                 highest level of
                                                 resilience offered by
                                                 Northgate
                                                 Information
                                                 Solutions. This builds
                                                 on the ‘failsafe’
                                                 technology but
                                                 automatically detects
                                                 primary system
                                                 failure. Should the
                                                 primary fail, the
                                                 secondary is
                                                 automatically re-
                                                 configured as the
maintained on different disks on     primary and users are switched
the same system. The ‘live’          to it. Users are automatically
database records all updates         logged on to the top level of
via transaction logging whilst       their current application so that
the second or ‘shadow’               they can continue working with
database remains unmounted           minimal disruption to service.
and unavailable to users.
At a time convenient to              The above features are
individual sites, the ‘shadow’       available on Windows, UNIX
database is mounted and the          and Linux platforms.
transaction logs are replayed to
keep the database in step with
the ‘live’ one. Shadow Database
avoids the lengthy processes of      In summary
restoring a database enabling
the system to become available       Great leaps have been taken by
for use quicker. The ‘failed’        vendors of Multivalue
database can then be                 databases in the last few years
recovered without impacting on       including fully protected
the user community.                  journaled filing systems,
                                     standby databases and failsafe
Failsafe provides a high level       machines which can effectively
of resilience by mirroring           look after themselves. All of
databases across separate            which, when coupled with the