Restore may hang if the database contains more than 4 billion records
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Key: CORE-5228
URL: http://tracker.firebirdsql.org/browse/CORE-5228
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 3.0.0, 4.0 Initial, 2.5.5, 2.5.4, 2.5.3 Update 1, 2.1.7,
2.5.3, 2.5.2 Update 1, 2.5.2, 2.5.1, 2.5.0
Reporter: Dmitry Yemanov
The problem of the current restore process is that every record is inserted in
its own looper roundtrip and thus using its own savepoint. The savepoint number
is 32-bit and it wraps around after 2^32 iterations. This particular issue is
not related to GBAK, it's common to any single transaction modifying billions
of records. Fortunately, old dumb savepoint handling is tolerate to such a
wraparound in trivial cases, so GBAK is not affected.
Second part of the problem appears when this transaction has also a deferred
work (uncommitted DDL). AFAIU, the legacy code implicitly assumes that there
cannot be savepoint number zero, but it becomes possible due to wraparound. So
DFW_merge_work() is called with old_sav_number = 0 and new_sav_number = 0 and
it enters an infinite loop, causing a hang.
Workaround for GBAK's restore is to use the -o switch, which restores every
table in its own transaction (and also separates a DDL transaction from
multiple DML transactions).
A noticable improvement could be to avoid savepoints during restore at all.
IIRC, InterBase has added the isc_tpb_no_savepoints feature. But I leave this
for another ticket.
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