B-tree Locking

• Root lock on a B-tree is a bottleneck

• Use tree locking to relieve it

• Problem: node splits

• So, don’t unlock a node till you’re sure its child won’t split (i.e. has space for an insert)

• Implies different locking rules for different ops(search vs. insert/update)

If you unlock P before splitting C,

then you have to back up and lock

P again, which breaks the tree

locking protocol.

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