Subject Re[2]: [Firebird-devel] [firebird-support] Re : Sweep process too many writes to disc
Author Александр Пешков
>> Sweep work in this way or such different? If yes i should see many reads and
>> > only few writes to disk but this not happend. I see >1TB writes to disc
>> > for db size 52.74GB.
>> >

>I think the key issue that Karol is pointing to is the ratio of Disk IO writes to the number of pages (size of database). I agree with him.
>Even if there are off-page changes, these could be collected into a page group and written to disk as a group (since all of the extra pages are only related to the single original page).

As any regular DB access sweep collects pages in groups. But no matter of it I'm absolutely not surprised with such ratio. When record on a data page is garbage collected a lot of other pages are touched - indices for example. And as long as we do not expect removed versions on a page to be in index order number of index pages modified (and therefore written) is equal to the number of removed versions with different index key values. I.e. ratio == 20 is quite possible.

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