uber / cherami-server / 2795

// Copyright (c) 2016 Uber Technologies, Inc.

//

// Permission is hereby granted, free of charge, to any person obtaining a copy

// of this software and associated documentation files (the "Software"), to deal

// in the Software without restriction, including without limitation the rights

// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

// copies of the Software, and to permit persons to whom the Software is

// furnished to do so, subject to the following conditions:

//

// The above copyright notice and this permission notice shall be included in

// all copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

// THE SOFTWARE.

package storehost

import (

        "math"

        "time"

        "github.com/uber/cherami-server/storage"

        "github.com/uber/cherami-thrift/.generated/go/cherami"

        "github.com/uber/cherami-thrift/.generated/go/store"

)

const (

        // special sequence numbers

        // used as the seal-seqnum that indicates that the extent is

        // not sealed

        seqNumNotSealed = int64(math.MaxInt64)

        // used as the seal-seqnum to indicate that extent was sealed

        // at an unspecified seqnum

        seqNumUnspecifiedSeal = int64(math.MaxInt64 - 1)

        // the max allowed seqnum (subject to mode-specific bitmask)

        seqNumMax = int64(math.MaxInt64 - 2)

)

        }

}

// The 64-bit key (or 'address') needs to be _unique_ within the DB for a given

// extent.  To ensure the key is unique, we encode it using the "visibility"

// (or deliver-at) time and the (unique) sequence-number.

//

// For timer-queues, the visibility time would be the sum of the enqueue-time

// on the message and the specified delay. For append-queues, the visibility

// time could be thought to be equal to the enqueue-time, since the messages

// are ready to be delivered as soon as they were received.

// Encoding the timestamp in the key helps with two things:

// 1. we are able to determine if the message is ready to be delivered; which

//    is more important in the timer-queue scenario, since with append-queue

//    the timestamp would always be in the past.

// 2. when we receive a GetAddressFromTimestamp call, we would do a "Seek()"

//    on the underlying storage with a key that uses the provided timestamp

//    (which, btw, is in "seconds" granularity) and a "0" seqNum.

// NB: More the number of bits we use for seq-num, the less 'precise' would the

// visibility time be. That said, the number of bits for seq-num should never be

// greater than '30' (1 second ~= 2^30 nanoseconds), since we would lose the

// "second" level granularity on the delay)

type modeSpecificCallbacks interface {

        messageVisibilityTime(msg *store.AppendMessage) (visibilityTime int64)

        constructKey(visibilityTime int64, seqNum int64) (key storage.Key)

        deconstructKey(key storage.Key) (visibilityTime int64, seqNum int64)

        maxSeqNum() (seqNum int64)

        constructSealExtentKey(seqNum int64) (key storage.Key)

        deconstructSealExtentKey(key storage.Key) (seqNum int64)

        isSealExtentKey(key storage.Key) bool

}

const (

        // for timer-queues, use 38 bits of (visibiilty) timestamp, 26 bits of seqnum

        timerQueueSeqNumBits = 26

        // for append-queues, use 38 bits of timestamp, 26 bits of seqnum

        appendQueueSeqNumBits = 26 // 38 bits timestamp, 26 bits seqnum

)

// -- timer queue helper routines -- //

type timerQueueCallbacks struct {

        seqNumMax        int64 // max seq-num

        seqNumBitmask    int64 // bitmask for seqnum

        timestampBitmask int64 // bitmask for timestamp

}

}

// -- append queue helper routines -- //

type appendQueueCallbacks struct {

        seqNumMax        int64 // max seq-num

        seqNumBitmask    int64 // bitmask for seqnum

        timestampBitmask int64 // bitmask for timestamp

}

}