From: Thomas Sanders Date: Fri, 24 Mar 2017 16:16:10 +0000 (+0000) Subject: oxenstored: do not commit read-only transactions X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~2392^2~2 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=b2a4105820807beb85cfeeaf2dc3c8bb93cc6d0c;p=xen.git oxenstored: do not commit read-only transactions The packet telling us to end the transaction has always carried an argument telling us whether to commit. If the transaction made no modifications to the tree, now we ignore that argument and do not commit: it is just a waste of effort. This makes read-only transactions immune to conflicts, and means that we do not need to store any of their details in the history that is used for assigning blame for conflicts. We count a transaction as a read-only transaction only if it contains no operations that modified the tree. This means that (for example) a transaction that creates a new node then deletes it would NOT count as read-only, even though it makes no change overall. A more sophisticated algorithm could judge the transaction based on comparison of its initial and final states, but this would add complexity and computational cost. Signed-off-by: Thomas Sanders Reviewed-by: Jonathan Davies --- diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml index 88fea3467a..c1511c0771 100644 --- a/tools/ocaml/xenstored/process.ml +++ b/tools/ocaml/xenstored/process.ml @@ -378,6 +378,7 @@ let do_transaction_end con t domains cons data = | x :: _ -> raise (Invalid_argument x) | _ -> raise Invalid_Cmd_Args in + let commit = commit && not (Transaction.is_read_only t) in let success = let commit = if commit then Some (fun con trans -> transaction_replay con trans domains cons) else None in History.end_transaction t con (Transaction.get_id t) commit in diff --git a/tools/ocaml/xenstored/transaction.ml b/tools/ocaml/xenstored/transaction.ml index edd1178d80..8f95301953 100644 --- a/tools/ocaml/xenstored/transaction.ml +++ b/tools/ocaml/xenstored/transaction.ml @@ -128,6 +128,7 @@ let make ?(internal=false) id store = let get_store t = t.store let get_paths t = t.paths +let is_read_only t = t.paths = [] let add_wop t ty path = t.paths <- (ty, path) :: t.paths let add_operation ~perm t request response = if !Define.maxrequests >= 0