Re: [Firebird-devel] Firebird 2.5: Performance degradation and increasing file size

[Alexander P. <pes...@ma...>]

On Wednesday 06 January 2010 21:39:40 Ann W. Harrison wrote:
> Alexander Peshkoff wrote:
> >> ... its slightly interesting
> >> that the file sizes are exactly the same for the database after
> >> it's been backed up and restored and the first run.
> >
> > Provided empty database is restored once again (remember, all tables were
> > dropped), may be it can the same.
>
> The reason that's interesting is that there is a difference in growth
> between runs - and the runs are identical.  Why would two series have
> exactly the same growth in each run?
>
>   Run    Database Size   Bytes of
>              Bytes	 Growth
>   7       19,505,152     2,224,128
>   5       14,413,824     2,392,064
>   8       22,016,000     2,510,848
>   2        6,180,864     2,580,480
>   3        8,884,224     2,703,360
>   1        3,600,384     2,797,568
>   9       24,846,336     2,830,336
>   6       17,281,024     2,867,200
>   4       12,021,760     3,137,536
> 10       28,045,312     3,198,976

Really surprising. I have not noticed this fact.

Also please pay attention - the fact that server does not reuse pages 
after 'DROP TABLE' does not explain performance degradation. If for any run 
each table containt X pages, why should we have visible performance 
difference when this pages are located in the beginning of the file or in the 
end of it. Specially well seen in series 11-20 from original Gary's letter.