Deadlock is possible when two data pages contains record fragments pointing to
each other
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Key: CORE-4372
URL: http://tracker.firebirdsql.org/browse/CORE-4372
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 3.0 Alpha 2, 3.0 Alpha 1, 2.5.2 Update 1, 2.1.5 Update 1,
2.5.2, 2.1.5, 2.5.1, 2.1.4, 2.5.0, 2.1.3, 2.1.2, 2.1.1, 2.1.0
Reporter: Vlad Khorsun
Below is typical case when deadlock happens.
Note, lock table dump and memory dump was produced (by custom build of FB 2.5)
at moment when deadlock is detected by lock manager.
Therefore both dumps are consistent with each other.
First, look at lock table dump:
LOCK BLOCK 15127944
Series: 3, Parent: 26520, State: 3, size: 8 length: 8 data: 0
Key: 0001:2386725, Flags: 0x00, Pending request count: 2
Hash que (23): forward: 1109840, backward: 2404168
Requests (3): forward: 15467224, backward: 17397008
Request 15467224, Owner: 4605016, State: 3 (3), Flags:
0x100
Request 33823352, Owner: 1406720, State: 0 (6), Flags:
0x22
Request 17397008, Owner: 22445704, State: 0 (3), Flags:
0x22
LOCK BLOCK 34415560
Series: 3, Parent: 26520, State: 3, size: 8 length: 8 data: 0
Key: 0001:2386706, Flags: 0x00, Pending request count: 2
Hash que (17): forward: 1595232, backward: 1221992
Requests (3): forward: 28400464, backward: 32840696
Request 28400464, Owner: 22445704, State: 3 (3), Flags: 0x100
Request 15282984, Owner: 29728544, State: 0 (6), Flags: 0x22
Request 32840696, Owner: 4605016, State: 0 (3), Flags: 0x22
Here owners 22445704 and 4605016 owns locks 34415560 and 15127944
correspondingly and acquires others lock at the same time.
This is classical deadlock.
Note, despite of compatible lock requests, it can't be granted because of
another non-compatible requests in high position in
pending request queue (by owners 1406720 and 29728544).
Lets look at memory dump to see how this happens:
a) owner 4605016 call DPM_fetch_fragment which call CCH_handoff (DP->DP)
2386725 -> 2386706
b) owner 22445704 call DPM_fetch_fragment which call CCH_handoff (DP->DP)
2386706 -> 2386725
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