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Just ran into this link, which seems to describe how MVCC can sometimes not be enough.

http://ronaldbradford.com/blog/understanding-innodb-mvcc-200...

Having read through it, I rather suspect that that's not a matter of writers blocking readers or the other way round, but instead a case of writers blocking writers - he's writing a lot of data to the table, and it's highly likely that InnoDB has escalated the lock to a table lock - which effectively prevents concurrent writes.

I don't believe that InnoDB escalates locks. Quoting from the fine manual:

http://dev.mysql.com/doc/refman/5.7/en/innodb-transaction-mo...

> InnoDB does locking on the row level and runs queries as nonlocking consistent reads by default, in the style of Oracle. The lock information in InnoDB is stored so space-efficiently that lock escalation is not needed: Typically, several users are permitted to lock every row in InnoDB tables, or any random subset of the rows, without causing InnoDB memory exhaustion.

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