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Displaying posts with tag: sys (reset)

When your query is blocked, but there is no blocking query
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When I queried information_schema.innodb_trx (introduced in 5.1 with the InnoDB Plugin) I noticed there were a few transactions in LOCK WAIT state.

Example:
mysql [information_schema] > select trx_id,trx_state 
    -> from information_schema.innodb_trx;
+--------+-----------+
| trx_id | trx_state |
+--------+-----------+
| 7974 | LOCK WAIT |
| 7962 | RUNNING |
+--------+-----------+
2 rows in set (0.00 sec)

Then I made a query to join a few information_schema and performance_schema tables to find out which query was blocking my transactions. It turned out that the blocking transaction had a trx_query=NONE. So my query was block by a transaction doing nothing. That's not really helpful.

Let's try to recreate the situation and see exactly what happened. I'll use













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ps_helper and its migration to sys
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MySQL’s Performance Schema is an incredibly rich and versatile instrumentation engine, but apparently, with great power, comes increased complexity for the user to understand up front.

I think this is pretty natural:

  • The more flexibility you provide to the user on what to monitor (and this is one of the major goals of Performance Schema) – the more there is to twiddle from a configuration perspective.
  • The more data we provide in as generic a ways as possible – the more data there is.

Performance Schema is also only going to grow over time. There are many many missing bits of

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