Commits on Oct 7, 2024

1. khepri_tree: Add an option to accumulate keep-while expirations …

   This change adds a type `khepri:delete_options()` similar to
   `khepri:put_options()` which includes a new option
   `return_keep_while_expirations`. Setting this option in a call to
   `khepri_adv:delete_many/3` or `khepri_tx_adv:delete_many/2` will include
   any tree nodes deleted because of expired keep-while conditions in the
   `khepri_adv:many_results()` return value.
   
   In order to accumulate these deletions we need to modify
   `khepri_machine:remove_expired_nodes/2` slightly to pass the fold
   function and accumulator for the current `#walk{..}`.
   
   This option is useful for callers if they need to do something with any
   tree nodes which were deleted by keep-while conditions. For example in
   RabbitMQ we currently delete all bindings which are associated with a
   queue in a transaction. Bindings should always be removed when their
   associated queue is removed so they seem like an ideal case to use a
   keep-while condition. We send notifications and invoke callbacks with
   the set of bindings which were deleted though, so we need to return
   these deleted records. With this change we can avoid performing binding
   deletion in a transaction and instead only delete the queue record while
   providing the new option. This is significantly more efficient because
   of the way the Khepri store is organized in RabbitMQ.

   

   the-mikedavis committed Oct 7, 2024
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