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...

Code Block
type immutablemap_string2string struct{
    storemap    map[string]string
}

func (imstr2str * immutablemap_string2string) get(key string) (string, error){
    rstr,ok := imstr2str.storemap[key]
    if(!ok){
        return nil, fmt.Errorf("key not exist")
    }
    return rstr, nil
}

func (imstr2str * immutablemap_string2string) put(key string, val string) (string, error){
    return nil, fmt.Errorf("not allowed put in immutablemap")
}

type metatable struct{
    ...
    ts2alias2name map[Timestamp]immutablemap_string2string
    newestAliasTs Timestamp
    ...
}
  • GetCollectionByName add alias timestamp as parameter to select which alias2name map will be used in ts2alias2name.
  • Change to alias will add a new alias2name immutable map in ts2alias2name.
Code Block
func build(im * immutablemap_string2string) Builder{
    builder := &Builder{
        reference: im
        mutable:   nil
    }
    return builder
}

//struct to bulid a new immutablemap according to the exist version
type Builder struct{
    reference    immutablemap_string2string
    mutable      map[string]string
}

func (bdr *Builder) maybeClone(){
    if bdr.reference != nil{
        bdr.mutable = make(map[string]string)
        for k,v := range bdr.reference.storemap{
            bdr.mutable[k] = v
        }
        
        bdr.reference = nil
    }
}

func (bdr *Builder) getnamefromalias(key string) (string, bool){
    bdr.maybeClone()
    return bdr.mutable[key]
}

func(bdr *Builder) putalias2name(key string, val string) (string, bool){
    bdr.maybeclone()
    var pre string
    if v,ok = bdr.mutable[key], ok{
        pre = v
    }else{
        pre = nil
    }
    bdr.mutable[key] = val
    return pre, ok
}

func(bdr *Builder) removealias2name(key string) (string, bool){
    bdr.maybeclone()
    var pre string
    if v,ok = bdr.mutable[key], ok{
        pre = v
        delete(bdr.mutable, key)
    }else{
        pre = nil
    }
    return pre, ok
}

func (bdr *Builder) build() immutablemap_string2string{
    if bdr.reference != nil{
        reference := bdr.reference
        bdr.reference = nil
        return reference
    }else{
        mutable = bdr.mutable
        bdr.mutable = nil
        res := & immutablemap_string2string{
            storemap:mutable
        }
        return res
    }
}

func (mt * metatable) addAlias(collectionAlias string, collectionName string) (string, error){
    mt.ddLock.Lock()
    defer mt.ddLock.Unlock()
    ...
    ts = getTimestamp()
    tspre = mt.newestAliasTs
    Bdr = build(mt.ts2alias2name[tspre])
    pre,ok := Bdr.putalias2name(collectionAlias, collectionName)
    if ok{
        return pre, fmt.Errorf("alias already exist when add alias") 
    }
    mt.ts2alias2name[ts] = Bdr.build()
    mt.newestAliasTs = ts
    ...
    return nil, nil
}

func (mt * metatable) dropAlias(collectionAlias string) (string, error){
    mt.ddLock.Lock()
    defer mt.ddLock.Unlock()
    ...
    ts = getTimestamp()
    tspre = mt.newestAliasTs
    Bdr = build(mt.ts2alias2name[tspre])
    pre,ok := Bdr.removealias2id(collectionAlias)
    if !ok{
        return nil, fmt.Errorf("alias not exist when drop alias") 
    }
    mt.ts2alias2name[ts] = Bdr.build()
    mt.newestAliasTs = ts
    ...
    return pre, nil
}

func (mt * metatable) alterAlias(collectionAlias string, collectionName string) (string, error){
    mt.ddLock.Lock()
    defer mt.ddLock.Unlock()
    ...
    ts = getTimestamp()
    tspre = mt.newestAliasTs
    Bdr = build(mt.ts2alias2name[tspre])
    pre,ok := Bdr.putalias2name(collectionAlias, collectionName)
    if !ok{
        return nil, fmt.Errorf("alias not exist when alter alias") 
    }
    mt.ts2alias2name[ts] = Bdr.build()
    mt.newestAliasTs = ts
    ...
    return pre, nil
}
  • GetCollectionByName(), IsAlias(), ListAlias() ... which is related to alias will add alias timestamp as parameter to select which alias2name map will be used in ts2alias2name.
  • Users can't drop the collection if the collection is referenced by an alias

Change to globalMetaCache

  • Add a function fetchAliasCache to () to fetch the newestAliasTs and the corresponding alias2name from rootcoord into proxy if newestAliasTs is different with the stored timestamp in globalMetaCache.
  • When each proxy task begin to excute, running fetchAliasCache() to get the newestAliasTs and the corresponding alias2name from globalMetaCache to task environment.
  • When proxy task need a collecition name in task request, first check if the name is alias. If yes, replace it with the corresponding collecition name use gotten alias2name.
  • If we do this, the cache in globalMetaCache will be the map with key as collection real name and value as collection information. 
  • When proxy task refers to the rootcoord task, it's necessary to pass the cached newestAliasTs as the rootcoord task request in order to make the apis which is related with alias to select which alias2name they need to use.

Compatibility, Deprecation, and Migration Plan

Above changing plan will add a item in rootcoord task request, which may need some attention.

Test Plan

  • Unit tests

References