14 GB less in database size after migrating from FB 3.0 to FB 5.0

[Tomasz Dubiel]

Hello.

Have you ever experienced such database size reduction? It's not just about backup and restore, because there is no size difference when restoring on FB 3.0.

On the database state 3 months ago 31 526 684 records from one table take 24,5 GB

and now on FB 5.0 33 027 910 records take 9 GB. Quite unexpected for us.

Best regards.

[Dimitry Sibiryakov]

Tomasz Dubiel wrote 22.06.2026 13:27:
> On the database state 3 months ago 31 526 684 records from one table take 24,5 GB
> and now on FB 5.0 33 027 910 records take 9 GB. Quite unexpected for us.

Why don't you just compare stats to see average page fill and record version
length?..

--
WBR, SD.

[Tomasz Dubiel]

[Dimitry Sibiryakov]

Tomasz Dubiel wrote 22.06.2026 13:37:
> poniedziałek, 22 czerwca 2026 o 13:32:32 UTC+2 sd napisał(a):

I said "compare", not "post here random pictures".

--
WBR, SD.

[Omacht András]

Tomasz,

 

look at „Compresson”:

45,99 (3,0) vs. 150,4

 

András

 

 

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[Tomasz Dubiel]

OK, but what can be the reason of such difference?

Best regards.

[Mark Rotteveel]

Do you have a lot of long (VAR)CHAR fields (especially if UTF8) that in
practice are NULL or have relatively short values? If so, this might be
the result of the improved RLE compression in Firebird 5.0 [1].

Mark


[1]:
https://firebirdsql.org/file/documentation/release_notes/html/en/5_0/rlsnotes50.html#rnfb50-engine-rle

--
Mark Rotteveel

[Dimitry Sibiryakov]

Tomasz Dubiel wrote 22.06.2026 13:49:
> OK, but what can be the reason of such difference?

May be https://github.com/FirebirdSQL/firebird/issues/4723 which Google AI
found for me.

--
WBR, SD.

[Tomasz Dubiel]

Thank you all very much :-). It's probably the case.

[Tomasz Dubiel]

It's about the column:

COROBIONO              T_MAXSTRING /* T_MAXSTRING = VARCHAR(32765) */,

[Mark Rotteveel]

On 22-06-2026 14:18, Tomasz Dubiel wrote:
> It's about the column:
> COROBIONO              T_MAXSTRING /* T_MAXSTRING = VARCHAR(32765) */,

Yes, that will do it (especially if often NULL, or with relatively short
actual values).

Mark
--
Mark Rotteveel