Don't use get_lock in the default implementation. #5
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get_lock() changes behaviour in MySQL 5.7, which causes in turn causes workers to lock more rows than necessary. This patch changes the behavior of Data::Consumer::MySQL2 to claim rows by doing SELECT followed by UPDATE, instead of two SELECTs (second select was necessary to validate result of GET_LOCK() since it wasn't atomic, and was a major change from Data::Consumer::MySQL). SELECT followed by UPDATE allows two claim strategies to be implemented, both relying on implicit database locks: atomic CAS (used by default) and SELECT FOR UPDATE.
davydovmax
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Without a fix, if we encounter this scenario, we will get an infinite loop in acquire():
1. start consuming
2. explicitly ignore() any item
3. continue consuming
4. wait till reset() is called (queue is exhausted or consume() called again)
4. try consume more items
5. acquire() receives already ignored item
6. item is ignored but $self->{last_id} is not updated
7. we skip item and loop back to demerphq#5, where process same item again
Fix just updates $self->{last_id} when we skip an ignored item. This
logic is similar to original logic in Data::Consumer::MySQL.
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What do you think of https://github.com/demerphq/Data-Consumer/tree/remove-get-lock-2 It looks to me we need to take some defensive measures before we can merge this. See #7 |
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Fixes #4
get_lock() changes behaviour in MySQL 5.7, which causes in turn causes
workers to lock more rows than necessary.
This patch changes the behavior of Data::Consumer::MySQL2 to claim rows
by doing SELECT followed by UPDATE, instead of two SELECTs (second
select was necessary to validate result of GET_LOCK() since it wasn't
atomic, and was a major change from Data::Consumer::MySQL).
SELECT followed by UPDATE allows two claim strategies to be implemented,
both relying on implicit database locks: atomic CAS (used by default)
and SELECT FOR UPDATE.