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Restore may hang if the database contains more than 4 billion records [CORE5228] #5507

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firebird-issue-importer opened this issue May 6, 2016 · 3 comments

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firebird-issue-importer commented May 6, 2016

Submitted by: @dyemanov

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.

Commits: dce0b4c 522f4c0

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firebird-issue-importer commented May 6, 2016

Modified by: @dyemanov

assignee: Dmitry Yemanov [ dimitr ]

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firebird-issue-importer commented May 6, 2016

Modified by: @dyemanov

status: Open [ 1 ] => Resolved [ 5 ]

resolution: Fixed [ 1 ]

Fix Version: 3.0.1 [ 10730 ]

Fix Version: 4.0 Alpha 1 [ 10731 ]

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firebird-issue-importer commented May 15, 2016

Modified by: @pavel-zotov

status: Resolved [ 5 ] => Resolved [ 5 ]

QA Status: No test => Cannot be tested

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