Current state: Disccusion completed
ISSUE: https://github.com/milvus-io/milvus/issues/17131
PRs: TODO
Keywords: Collection Alias, Atomic Switching
Released: TODO
RootCoordinator, Proxy, and all the key components, CollectionName and CollectionAlias are equal. MetaTable.GetCollectionByName(collectionName string, ts typeutil.Timestamp) can receive CollectionAlias and return corresponding CollectionInfo.CollectionAlias ∧ CollectionName = ∅ . CollectionAlias cannot collide with existing CollectionNames.CollectionAlias works as an extra pointer to the existing collection in the RootCoordinator, we can implement collection hot reloading at a low cost.AddAlias, DropAlias and AlterAlias, the change of relationship between alias and collection should not affect the operations online, i.e. these operations shoud use the relationship when the task begin to excute.AddAlias, DropAlias and AlterAlias, all proxy should receive the change in the same timestamp to ensure the atomicity between the proxy cache and the rootcoord data.collection if the collection is referenced by an alias, which can simplify the operation and make it easier to ensure the atomicity property about alias changes.Metatable now add ts2alias2name and newestAliasTs member variablestype immutablemap_string2string struct{
storemap map[string]string
}
func (imstr2str * immutablemap_string2string) get(key string) (string, error){
rstr,ok := imstr2str.storemap[key]
if(!ok){
return "", fmt.Errorf("key not exist")
}
return rstr, nil
}
func (imstr2str * immutablemap_string2string) put(key string, val string) (string, error){
return "", fmt.Errorf("not allowed put in immutablemap")
}
type metatable struct{
...
ts2alias2name map[Timestamp]immutablemap_string2string
newestAliasTs Timestamp
...
} |
alias2name immutable map in ts2alias2name.func build(im typeutil.ImmutablemapString2string) *Builder {
builder := &Builder{
reference: im,
mutable: nil,
}
return builder
}
type Builder struct {
reference typeutil.ImmutablemapString2string
mutable map[string]string
}
func (bdr *Builder) maybeClone() {
if !bdr.reference.IsEmpty() {
bdr.mutable = make(map[string]string)
for k, v := range bdr.reference.GetCopy() {
bdr.mutable[k] = v
}
bdr.reference = typeutil.ImmutablemapString2string{}
} else {
bdr.mutable = make(map[string]string)
}
}
func (bdr *Builder) getnamefromalias(key string) (string, bool) {
bdr.maybeClone()
rstr, rbool := bdr.mutable[key]
return rstr, rbool
}
func (bdr *Builder) putalias2name(key string, val string) (string, bool) {
bdr.maybeClone()
var pre string
v, ok := bdr.mutable[key]
if ok {
pre = v
} else {
pre = ""
}
bdr.mutable[key] = val
return pre, ok
}
func (bdr *Builder) removealias2name(key string) (string, bool) {
bdr.maybeClone()
var pre string
v, ok := bdr.mutable[key]
if ok {
pre = v
delete(bdr.mutable, key)
} else {
pre = ""
}
return pre, ok
}
func (bdr *Builder) Build() typeutil.ImmutablemapString2string {
if !bdr.reference.IsEmpty() {
reference := bdr.reference
bdr.reference = typeutil.ImmutablemapString2string{}
return reference
}
mutable := bdr.mutable
bdr.mutable = nil
res := typeutil.NewImmutablemapString2string(mutable)
return res
}
func (mt * metatable) addAlias(collectionAlias string, collectionName string) error{
mt.ddLock.Lock()
defer mt.ddLock.Unlock()
...
ts = getTimestamp()
tspre = mt.newestAliasTs
Bdr = build(mt.ts2alias2name[tspre])
_,ok := Bdr.putalias2name(collectionAlias, collectionName)
if ok{
return fmt.Errorf("alias already exist when add alias")
}
mt.ts2alias2name[ts] = Bdr.build()
mt.newestAliasTs = ts
...
return nil
}
func (mt * metatable) dropAlias(collectionAlias string) error{
mt.ddLock.Lock()
defer mt.ddLock.Unlock()
...
ts = getTimestamp()
tspre = mt.newestAliasTs
Bdr = build(mt.ts2alias2name[tspre])
_, ok := Bdr.removealias2id(collectionAlias)
if !ok{
return fmt.Errorf("alias not exist when drop alias")
}
mt.ts2alias2name[ts] = Bdr.build()
mt.newestAliasTs = ts
...
return nil
}
func (mt * metatable) alterAlias(collectionAlias string, collectionName string) error{
mt.ddLock.Lock()
defer mt.ddLock.Unlock()
...
ts = getTimestamp()
tspre = mt.newestAliasTs
Bdr = build(mt.ts2alias2name[tspre])
_,ok := Bdr.putalias2name(collectionAlias, collectionName)
if !ok{
return fmt.Errorf("alias not exist when alter alias")
}
mt.ts2alias2name[ts] = Bdr.build()
mt.newestAliasTs = ts
...
return 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.collection if the collection is referenced by an aliasfetchAliasCache() to fetch the newestAliasTs and the corresponding alias2name from rootcoord into proxy if newestAliasTs is different with the stored timestamp in globalMetaCache.fetchAliasCache() to get the newestAliasTs and the corresponding alias2name from globalMetaCache to task environment.alias2name.globalMetaCache will be the map with key as collection real name and value as collection information. 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.Above changing plan will add a item in rootcoord task request, which may need some attention.