Corruption risk on drop table with non exclusive connection
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Key: CORE-6073
URL: http://tracker.firebirdsql.org/browse/CORE-6073
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 3.0.4, 2.5.8
Environment: Any, as far as I understand.
Reporter: Kjell Rilbe
Priority: Critical
I have once suffered database corruption due to dropping tables when other
users were working with the same database. IBSurgeon helped med repair it, and
explained that drop table should be considered an exclusive action, i.e.
perform only under exclusive connection.
According to them, the problem still exists in latest released versions 2.5 and
3.0, not sure about 4.0.
This is from Alexey Kovyazin of IBSurgeon in May 2019:
"We know, that drop table during the active users work leads to corruption, but
we don't have reproducible test case, only corrupted databases from the people
who used to drop tables.
It looks like the reason of the corruption is the interrupted DROP TABLE
command - it does not complete properly - data, pointer and index root pages
are deleted, but records in RDB$PAGES/RDB$RELATIONS/RDB$RELATION_FIELDS/etc
remain.
After that, the access to the partially deleted table is not possible - it
gives error "wrong page type expected 4, found XX".
Right now, we don't have time to create the test case to reproduce it -
theoretically, it could be some fork of firebird-oltp-test with
create-drop-create cycle."
I wish I could create a test case, but just maybe the description of the error
would hint at some part of the code?
Anyway, until fixed, I would suggest that the problem be documented in release
notes and drop table command documentation, with a recommendation to drop table
only in exclusive mode.
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