Metadata Locking and Deadlock Detection in MySQL 5.5
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Transcript of Metadata Locking and Deadlock Detection in MySQL 5.5
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Metadata locking inMySQL 5.5
Konstantin OsipovEngineer @ Mail.Ru
These slides released under the Creative Commons AttributionNoncommercialShare Alike License
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Mastering a 25-foot saw
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DDL vs. DML: an illustration
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What if... a transactional catalog
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Locking agents
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Define the problem (2)
Four groups of bugs:
- ALTER, DROP violate ACID
- … or ... break replication
- deadlocks in LOCK TABLES, FLUSH,
SET GLOBAL read_only and ALTER
- DML doesn't scale or THANK YOU
LOCK_open
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Define the problem (3)
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In come metadata locks
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Deadlock detection
How does a typical wait-for grpah look like?
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How to plug in
Engines need to plug-in to avoid cross-storage-
engine deadlocks.
- it's safe to #include “mdl.h”, no extra deps
- subclass MDL_waitfor_subgraph to accept
- MDL_waitfor_graph_visitor
- let us know when you're waiting, by calilng
- MDL_context::will_wait_for()
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Performance impact
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The roadmap
- help us add cross-storage-engine deadlock
detection!
- thr_lock.c and handler::store_lock() need not be
mandatory any more
- consistent DDL across all NDB cluster
- shard MDL_set (performance++)
- instrumentation
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Performance impact
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That's it.
Thank you for coming!
Further reading: WL#3873, WL#3726, WL#4284Mdl.pdf is available in MySQL internals manual.