Details
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Task
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Status: Open (View Workflow)
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Major
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Resolution: Unresolved
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None
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None
Description
as an alternative or functional replacement to Seconds_behind_master.
The request comes from salle of MariaDB support.
Attachments
Activity
bnestere, salle, as noted practically (thanks to pandi.gurusamy who pointed to that) we have had this feature in form of
GTIDs_behind_master = ShowSlaveStatus::Gtid_IO_Pos - @@global.gtid_slave_pos
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I'd close the ticket.
The show slave status also has the ShowSlaveStatus::Gtid_Slave_Pos. May be we just need to introduce a new variable in SSS to compute the difference?
No, in the general case, you cannot just subtract the sequence numbers of GTIDs to know how many GTIDs are pending.
Sure, but one can subtract in the gtid_strict_mode, which is always recommended.
What about tracking the number of transactions/GTIDs that remain un-executed in the relay log (e.g. incremented when the IO thread queues a GTID event, and decremented when SQL thread/worker commit a trx)?
In my humble opinion a message like:
"N transactions behind the master"
is much better indicator than Seconds_behind_master.
1000 seconds behind can mean single long running transaction whereas 15 seconds behind can mean 40 transactions behind. A DBA could be concerned more about slave lag of 40 transactions than about 1 transaction lag. This will also allow for better alerts by monitoring tools.