sharding: abort if target db becomes readonly before cutover #58
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fjordan
reviewed
Aug 10, 2018
| @@ -169,3 +169,10 @@ func NewMysqlPosition(file string, position uint32, err error) (mysql.Position, | |||
| }, nil | |||
| } | |||
| } | |||
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| func CheckDbIsAReplica(db *sql.DB) (bool, error) { | |||
| row := db.QueryRow("SELECT @@read_only") | |||
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Have we thought about using SHOW SLAVE STATUS here instead of just relying on the @@read_only variable? It seems it is technically possible to run an async slave without setting this flag as MySQL doesn't force you to set read_only = ON. What do you think?
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Shopify runs a master-master configuration which means masters from different location are slaving off each other (and hence SLAVE STATUS will show the slave thread on both instances). We're tracking making this configurable in #53
fjordan
approved these changes
Aug 10, 2018
fw42
approved these changes
Aug 13, 2018
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Follow up to #51
The rationale for this one is that it's too risky to go into the cutover phase if the target db is read-only anyway. It replaces a call that we previously did on the shop mover side.
@Shopify/pods