database administration need more help

[prem_4]

hi all!

once again i thank u all for ur replies for my last post.
i asked about important parameters that would assist database administration and i got many answers of which i have clarifications on 2 things :

1) Time for database to get ready
2) Time for database to recover from crash.

can anyone help me in finding it out?
any hints ?

[Yair Goldel]

Hi
Its depend in a lot off things like machine,storage,database size etc.

can you give us more details ?

[Yair Goldel]

Hi
Its depend in a lot off things like machine,storage,database size etc.

can you give us more details ?

[prem_4]

well thats good but can u put a knot between these factors - " machine, storage and database size" so that i can arrive at finding the time for database to get ready and the time for database to recover from crash!

time for database to get ready possibly means the amount of time the database takes to accept user commands after start up or after finishing a previous task.

the time for database to recover from crash must be the time it takes to automatically recover from any internal failure!!!

well these two things are suggested by another person amongst us and i am new to MySql so i have little knowledge of what they actually mean.

i am very much in need of ur help!

[Paula J Frazer-Campbell]

HI


The only way to find this out is to test and measure.


1) Time for database to get ready
2) Time for database to recover from crash

Paula

[Massimo Bianchi]

Hi,
in oracle there is a file, called alert_.log, which reports the times you need.

Usually there is a similar file, a log of the server, for every enterprise database, so you can check in it.

For startup time, usually is easy to find out.

For recovery time, it is a non-sense question, since it depends on the kind of crash. If you loose the disk, how logn does it take to you to re-build it ?

If you have to re-apply some logs, how many of them ? Are They on disk or you must search them in the tapes ?

So you can see that there are many non-timable questions to answer to...

HTH,
Massimo

[Yogeeraj_1]

hi,

In Oracle, we talk more in terms of:

Mean-Time-To-Recover (MTTR)
Where Database availability is a key issue for a DBA. In the event of a failure the DBA should strive to reduce the MTTR. This strategy ensures that the database is unavailable for the shortest possible amount of time. Anticipating the types of failures that can occur and using effective recovery strategies, the DBA can ultimately reduce the MTTR.

and

Mean-Time-Between-Failure (MTBF)
Where protecting the database against the various types of failures is also a key DBA task. To do this, a DBA must increase the Mean-Time-Between-Failures (MTBF). The DBA must understand the backup and recovery structures within an Oracle Database environment and configure the database so that failures will not occur often.

hope this helps!

regards
Yogeeraj

[Pete Randall]

1) Between 1 and 15 minutes

2) Between 5 and 1440 minutes


Pete

[twang]

Regarding time for an oracle database to recover from crash,
it depends on the checkpoints, frequent checkpoints will enable faster recovery.
How then should the DBA address this?
Depending on the number of datafiles in a database, a checkpoint can be a
highly resource intensive operation, since all datafile headers are frozen
during the checkpoint. There is a performance trade-off regarding frequency
of checkpoints. More frequent checkpoints enable faster database recovery
after a crash. This is why some customer sites which have a very low
tolerance for unscheduled system downtime will often choose this option.
However, the performance degradation of frequent checkpoints may not justify
this philosophy in many cases. Let's assume the database is up and running 95%
of the time, and unavailable 5% of the time from infrequent instance crashes
or hardware failures requiring database recovery. For most customer sites, it
makes more sense to tune for the 95% case rather than the rare 5% downtime.

[Paula J Frazer-Campbell]

Pete

Have you fully tested those times?

As if the database if female one must double your times.

And as for the crash, if airbags and side inpact bars are fitted the crash is not so bad.

Paula