AW: Journaling

[Fabian Kneubuehl]

Ivan,

 

Yes I know. But before you introduced this property in VServer.INI I called
DB.Flush() after each INSERT/DELETE/UPDATE and reading BLOBs and Pictures
from files.

 

Mit freundlichen Grüssen

Fabian Kneubühl

 

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Von: valentina-beta-bounces at lists.macserve.net
[mailto:valentina-beta-bounces at lists.macserve.net] Im Auftrag von Ivan
Smahin
Gesendet: Freitag, 20. April 2012 13:10
An: Valentina Beta
Betreff: Re: Journaling

 

 

On Apr 20, 2012, at 10:23 AM, Fabian Kneubuehl wrote:





Ruslan,

 

I used transaction control for concurrent DB changes in other DBs. E.g. If I
generate an invoice I start a TA, then I print the invoice. In the case the
printing fails, I rollback all TAs else I commit. So I guarantee, that the
invoices data are consistent. But flushing the DB was done by the DB itself
and not by my app!

 

 





The only secure strategy to prevent a huge data loss is to flush all DB
changes. Why does VServer not flush e.g. all x minutes (settable with a
property in VServer.INI) 

 

vServer has FlushEachDataChanges setting in the ini.

 

; 1 - Flush after any data modification.

; 0 - Default value - no flushing.

FlushEachDataChanges=0

 





and what happens if cache is full?

 

 

It is usual state of the cache. Assume that cache is full and we ask to load
one more db-page from the storage.

Firstly, we are trying to "unload" any (oldest) "unchanged" page (probably
not a single page but some set of pages to improve performance) from the
cache (obviously, such a page is not writing to the disk because it is not
changed).

If there are no "unchanged" pages in the cache then we have to "free" some
"dirty" page and such a page goes to the rollback journal first, and after
that, we write it down to the db storage. If some crash happens we know how
to restore the database to get rid of such a "dirty" changes.

 

 

-- 
Best regards,
Ivan Smahin
Senior Software Engineer
Paradigma Software, Inc
Valentina - The Ultra-Fast Database
http://www.valentina-db.com <http://www.valentina-db.com/> 

 

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