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Cosmos core events API (#49), remove rolling snapshots
* Reorganize, adding Batch structure * Rework stored procedure * Remove rolling snapshots * Add explicit non-indexed mode
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,105 @@ | ||
| namespace Equinox.Cosmos | ||
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| // NB this is a copy of the one in Backend - there is also one in Equinox/Infrastrcture.fs which this will be merged into | ||
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| open System | ||
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| /// Given a value, creates a function with one ignored argument which returns the value. | ||
| /// A backoff strategy. | ||
| /// Accepts the attempt number and returns an interval in milliseconds to wait. | ||
| /// If None then backoff should stop. | ||
| type Backoff = int -> int option | ||
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| /// Operations on back off strategies represented as functions (int -> int option) | ||
| /// which take an attempt number and produce an interval. | ||
| module Backoff = | ||
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| let inline konst x _ = x | ||
| let private checkOverflow x = | ||
| if x = System.Int32.MinValue then 2000000000 | ||
| else x | ||
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| /// Stops immediately. | ||
| let never : Backoff = konst None | ||
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| /// Always returns a fixed interval. | ||
| let linear i : Backoff = konst (Some i) | ||
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| /// Modifies the interval. | ||
| let bind (f:int -> int option) (b:Backoff) = | ||
| fun i -> | ||
| match b i with | ||
| | Some x -> f x | ||
| | None -> None | ||
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| /// Modifies the interval. | ||
| let map (f:int -> int) (b:Backoff) : Backoff = | ||
| fun i -> | ||
| match b i with | ||
| | Some x -> f x |> checkOverflow |> Some | ||
| | None -> None | ||
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| /// Bounds the interval. | ||
| let bound mx = map (min mx) | ||
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| /// Creates a back-off strategy which increases the interval exponentially. | ||
| let exp (initialIntervalMs:int) (multiplier:float) : Backoff = | ||
| fun i -> (float initialIntervalMs) * (pown multiplier i) |> int |> checkOverflow |> Some | ||
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| /// Randomizes the output produced by a back-off strategy: | ||
| /// randomizedInterval = retryInterval * (random in range [1 - randomizationFactor, 1 + randomizationFactor]) | ||
| let rand (randomizationFactor:float) = | ||
| let rand = new System.Random() | ||
| let maxRand,minRand = (1.0 + randomizationFactor), (1.0 - randomizationFactor) | ||
| map (fun x -> (float x) * (rand.NextDouble() * (maxRand - minRand) + minRand) |> int) | ||
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| /// Uses a fibonacci sequence to genereate timeout intervals starting from the specified initial interval. | ||
| let fib (initialIntervalMs:int) : Backoff = | ||
| let rec fib n = | ||
| if n < 2 then initialIntervalMs | ||
| else fib (n - 1) + fib (n - 2) | ||
| fib >> checkOverflow >> Some | ||
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| /// Creates a stateful back-off strategy which keeps track of the number of attempts, | ||
| /// and a reset function which resets attempts to zero. | ||
| let keepCount (b:Backoff) : (unit -> int option) * (unit -> unit) = | ||
| let i = ref -1 | ||
| (fun () -> System.Threading.Interlocked.Increment i |> b), | ||
| (fun () -> i := -1) | ||
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| /// Bounds a backoff strategy to a specified maximum number of attempts. | ||
| let maxAttempts (max:int) (b:Backoff) : Backoff = | ||
| fun n -> if n > max then None else b n | ||
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| // ------------------------------------------------------------------------------------------------------------------------ | ||
| // defaults | ||
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| /// 500ms | ||
| let [<Literal>] DefaultInitialIntervalMs = 500 | ||
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| /// 60000ms | ||
| let [<Literal>] DefaultMaxIntervalMs = 60000 | ||
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| /// 0.5 | ||
| let [<Literal>] DefaultRandomizationFactor = 0.5 | ||
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| /// 1.5 | ||
| let [<Literal>] DefaultMultiplier = 1.5 | ||
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| /// The default exponential and randomized back-off strategy with a provided initial interval. | ||
| /// DefaultMaxIntervalMs = 60,000 | ||
| /// DefaultRandomizationFactor = 0.5 | ||
| /// DefaultMultiplier = 1.5 | ||
| let DefaultExponentialBoundedRandomizedOf initialInternal = | ||
| exp initialInternal DefaultMultiplier | ||
| |> rand DefaultRandomizationFactor | ||
| |> bound DefaultMaxIntervalMs | ||
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| /// The default exponential and randomized back-off strategy. | ||
| /// DefaultInitialIntervalMs = 500 | ||
| /// DefaultMaxIntervalMs = 60,000 | ||
| /// DefaultRandomizationFactor = 0.5 | ||
| /// DefaultMultiplier = 1.5 | ||
| let DefaultExponentialBoundedRandomized = DefaultExponentialBoundedRandomizedOf DefaultInitialIntervalMs |
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