github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/meta/meta.go (about)

     1  // Copyright 2022 zGraph Authors. All rights reserved.
     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 meta
    16  
    17  import (
    18  	"sync"
    19  
    20  	"github.com/pingcap/errors"
    21  	"github.com/vescale/zgraph/internal/structure"
    22  	"github.com/vescale/zgraph/storage/kv"
    23  )
    24  
    25  // The globalIDMutex is used to reduce the global id key conflicts.
    26  var globalIDMutex sync.Mutex
    27  
    28  var (
    29  	mMetaKeyPrefix   = []byte("m")
    30  	mNextGlobalIDKey = []byte("next_global_id")
    31  	mNextIDKey       = []byte("next_id")
    32  	mGraphs          = []byte("graphs")
    33  	mGraphPrefix     = "graph"
    34  	mLabelPrefix     = "label"
    35  	mPropertyPrefix  = "property"
    36  )
    37  
    38  const (
    39  	// CurrentMagicByteVer is the current magic byte version, used for future meta compatibility.
    40  	CurrentMagicByteVer byte = 0x00
    41  	// PolicyMagicByte handler
    42  	// 0x00 - 0x3F: Json Handler
    43  	// 0x40 - 0x7F: Reserved
    44  	// 0x80 - 0xBF: Reserved
    45  	// 0xC0 - 0xFF: Reserved
    46  
    47  	// MaxInt48 is the max value of int48.
    48  	MaxInt48 = 0x0000FFFFFFFFFFFF
    49  	// MaxGlobalID reserves 1000 IDs. Use MaxInt48 to reserves the high 2 bytes to compatible with Multi-tenancy.
    50  	MaxGlobalID = MaxInt48 - 1000
    51  )
    52  
    53  // Meta is for handling meta information in a transaction.
    54  type Meta struct {
    55  	txn      *structure.TxStructure
    56  	StartVer kv.Version
    57  }
    58  
    59  // New returns a new instance of meta API object.
    60  func New(txn kv.Transaction) *Meta {
    61  	t := structure.NewStructure(txn, txn, mMetaKeyPrefix)
    62  	return &Meta{
    63  		txn:      t,
    64  		StartVer: txn.StartVer(),
    65  	}
    66  }
    67  
    68  // NewSnapshot returns a read-only new instance of meta API object.
    69  func NewSnapshot(snap kv.Snapshot) *Meta {
    70  	t := structure.NewStructure(snap, nil, mMetaKeyPrefix)
    71  	return &Meta{
    72  		txn:      t,
    73  		StartVer: snap.StartVer(),
    74  	}
    75  }
    76  
    77  // NextGlobalID generates next id globally.
    78  func (m *Meta) NextGlobalID() (int64, error) {
    79  	globalIDMutex.Lock()
    80  	defer globalIDMutex.Unlock()
    81  
    82  	newID, err := m.txn.Inc(mNextGlobalIDKey, 1)
    83  	if err != nil {
    84  		return 0, errors.Trace(err)
    85  	}
    86  	if newID > MaxGlobalID {
    87  		return 0, errors.Errorf("global id:%d exceeds the limit:%d", newID, MaxGlobalID)
    88  	}
    89  	return newID, err
    90  }
    91  
    92  // AdvanceGlobalID advances the global ID by n.
    93  // return the old global ID.
    94  func (m *Meta) AdvanceGlobalID(n int) (int64, error) {
    95  	globalIDMutex.Lock()
    96  	defer globalIDMutex.Unlock()
    97  
    98  	newID, err := m.txn.Inc(mNextGlobalIDKey, int64(n))
    99  	if err != nil {
   100  		return 0, err
   101  	}
   102  	if newID > MaxGlobalID {
   103  		return 0, errors.Errorf("global id:%d exceeds the limit:%d", newID, MaxGlobalID)
   104  	}
   105  	origID := newID - int64(n)
   106  	return origID, nil
   107  }
   108  
   109  // GenGlobalIDs generates the next n global IDs.
   110  func (m *Meta) GenGlobalIDs(n int) ([]int64, error) {
   111  	globalIDMutex.Lock()
   112  	defer globalIDMutex.Unlock()
   113  
   114  	newID, err := m.txn.Inc(mNextGlobalIDKey, int64(n))
   115  	if err != nil {
   116  		return nil, err
   117  	}
   118  	if newID > MaxGlobalID {
   119  		return nil, errors.Errorf("global id:%d exceeds the limit:%d", newID, MaxGlobalID)
   120  	}
   121  	origID := newID - int64(n)
   122  	ids := make([]int64, 0, n)
   123  	for i := origID + 1; i <= newID; i++ {
   124  		ids = append(ids, i)
   125  	}
   126  	return ids, nil
   127  }
   128  
   129  // GlobalID gets current global id.
   130  func (m *Meta) GlobalID() (int64, error) {
   131  	return m.txn.GetInt64(mNextGlobalIDKey)
   132  }