Re: [Firebird-devel] Collection of garbage in record with uncommitted version

[Vlad K. <hv...@us...>]

> 13.05.2014 13:36, Vlad Khorsun wrote:
>>     Yes
> 
>   How? If I remember your lesson right, garbage in a record is collected only if head 
> version is marked with transaction number lesser that OAT.

    This is a most often case. But, if you look at VIO_chase_record_version, you'll see
that concurrency (snapshot) transactions could pass not visible for them versions of record
and stop at some point. And in this point record version could be 
- visible for current tx
- mature for GC
- still have backversions

    In this case, cooperative GC could happen (i.e. purge will be called) before return to the
caller (VIO_next or VIO_data). 

 
>>      list_staying used to undo dead record version. It is not a most often operation.
> 
>   Actually, it is used in following cases:
> 
> 1) Undo with VIO_backout().
> 2) Undo of update_in_place() in VIO_verb_cleanup().
> 3) Applying third and following changes of the same record in one transaction.

    I know. I just a bit lazy when need to wrtite too much words, especially in Engilish :) 
In any case - all your points above is cases of undo operation.

Regards,
Vlad