github.com/matrixorigin/matrixone@v0.7.0/pkg/vm/engine/tae/logtail/service/waterline.go (about)

     1  // Copyright 2021 Matrix Origin
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //	http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package service
    16  
    17  import (
    18  	"sync"
    19  
    20  	"github.com/matrixorigin/matrixone/pkg/pb/timestamp"
    21  	"github.com/matrixorigin/matrixone/pkg/txn/clock"
    22  )
    23  
    24  // Waterliner maintains waterline for all subscribed tables.
    25  type Waterliner struct {
    26  	sync.Mutex
    27  
    28  	initialized bool
    29  	clock       clock.Clock
    30  
    31  	waterline timestamp.Timestamp
    32  }
    33  
    34  func NewWaterliner(clock clock.Clock) *Waterliner {
    35  	return &Waterliner{
    36  		initialized: false,
    37  		clock:       clock,
    38  	}
    39  }
    40  
    41  // Waterline returns waterline for subscribed table.
    42  //
    43  // it would be initialized on its first call.
    44  func (w *Waterliner) Waterline() timestamp.Timestamp {
    45  	w.Lock()
    46  	defer w.Unlock()
    47  
    48  	if !w.initialized {
    49  		now, _ := w.clock.Now()
    50  		w.waterline = now
    51  		w.initialized = true
    52  	}
    53  
    54  	return w.waterline
    55  }
    56  
    57  // Advance updates waterline.
    58  //
    59  // Caller should keep monotonous.
    60  func (w *Waterliner) Advance(update timestamp.Timestamp) {
    61  	w.Lock()
    62  	defer w.Unlock()
    63  
    64  	if !w.initialized {
    65  		panic("advance on uninitailized instance")
    66  	}
    67  
    68  	if update.Less(w.waterline) {
    69  		panic("timestamp rollback for waterline")
    70  	}
    71  
    72  	w.waterline = update
    73  }