UPDATE may hang when it does a full table scan and updates PK values

[spetrunia]

UPDATE may hang when it does a full table scan and updates PK values

[jkedgar]

I believe the issue is that each row is being updated over and over again (from id 1 to 101 to 201 to 301, etc.). In a previous database the solution was implemented in the SQL layer - if a key was being updated we did not allow that key to be used to find the rows to update - i.e. the optimizer was not allowed to select that path. Since MySQLonRocksDB can only access rows by their keys, maybe we need to have a flag that can indicate that a row has already been updated and as we come to each row to see if we should update it, skip those with the flag set.

[spetrunia]

Yes the cause is rows being updated over and over.

I don't think a flag would be needed - MyRocks is not the first MySQL storage engine to have this property. It just fails to inform the SQL layer that full table scan is actually scanning primary key.

I already have a patch, I'll commit it shortly.

[spetrunia]

https://reviews.facebook.net/D45519