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ddl_notifier: add subscription API (#56182)
ref #55722
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2024 PingCAP, Inc. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| package notifier | ||
|
|
||
| import ( | ||
| "context" | ||
| goerr "errors" | ||
| "fmt" | ||
| "time" | ||
|
|
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| "github.com/pingcap/errors" | ||
| sess "github.com/pingcap/tidb/pkg/ddl/session" | ||
| "github.com/pingcap/tidb/pkg/kv" | ||
| "github.com/pingcap/tidb/pkg/sessionctx" | ||
| "github.com/pingcap/tidb/pkg/util/logutil" | ||
| "go.uber.org/zap" | ||
| ) | ||
|
|
||
| // SchemaChangeHandler function is used by subscribers to handle the | ||
| // SchemaChangeEvent generated by the publisher (DDL module currently). It will | ||
| // be called at least once for every SchemaChange. The sctx has already started a | ||
| // pessimistic transaction and handler should execute exactly once SQL | ||
| // modification logic with it. After the function is returned, subscribing | ||
| // framework will commit the whole transaction with internal flag modification to | ||
| // provide exactly-once delivery. The handler will be called periodically, with | ||
| // no guarantee about the latency between the execution time and | ||
| // SchemaChangeEvent happening time. | ||
| // | ||
| // The handler function must be registered by RegisterHandler before the | ||
| // ddlNotifier is started. If the handler can't immediately serve the handling | ||
| // after registering, it can return nil to tell the ddlNotifier to act like the | ||
| // change has been handled, or return ErrNotReadyRetryLater to hold the change | ||
| // and re-handle later. | ||
| type SchemaChangeHandler func( | ||
| ctx context.Context, | ||
| sctx sessionctx.Context, | ||
| change *SchemaChangeEvent, | ||
| ) error | ||
|
|
||
| // ErrNotReadyRetryLater should be returned by a registered handler that is not | ||
| // ready to process the events. | ||
| var ErrNotReadyRetryLater = errors.New("not ready, retry later") | ||
|
|
||
| // HandlerID is the type of the persistent ID used to register a handler. Every | ||
| // ID occupies a bit in a BIGINT column, so at most we can only have 64 IDs. To | ||
| // avoid duplicate IDs, all IDs should be defined in below declaration. | ||
| type HandlerID int | ||
|
|
||
| const ( | ||
| // TestHandlerID is used for testing only. | ||
| TestHandlerID HandlerID = 0 | ||
| ) | ||
|
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| // RegisterHandler must be called with an exclusive and fixed HandlerID for each | ||
| // handler to register the handler. Illegal ID will panic. RegisterHandler should | ||
| // not be called after the global ddlNotifier is started. | ||
| // | ||
| // RegisterHandler is not concurrency-safe. | ||
| func RegisterHandler(id HandlerID, handler SchemaChangeHandler) { | ||
| intID := int(id) | ||
| // the ID is used by bit operation in processedByFlag. We use BIGINT UNSIGNED to | ||
| // store it so only 64 IDs are allowed. | ||
| if intID < 0 || intID >= 64 { | ||
| panic(fmt.Sprintf("illegal HandlerID: %d", id)) | ||
| } | ||
|
|
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| if _, ok := globalDDLNotifier.handlers[id]; ok { | ||
| panic(fmt.Sprintf("HandlerID %d already registered", id)) | ||
| } | ||
| globalDDLNotifier.handlers[id] = handler | ||
| } | ||
|
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||
| type ddlNotifier struct { | ||
| ownedSCtx sessionctx.Context | ||
| store Store | ||
| handlers map[HandlerID]SchemaChangeHandler | ||
| pollInterval time.Duration | ||
| } | ||
|
|
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| var globalDDLNotifier *ddlNotifier | ||
|
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| // InitDDLNotifier initializes the global ddlNotifier. It should be called only | ||
| // once and before any RegisterHandler call. The ownership of the sctx is passed | ||
| // to the ddlNotifier. | ||
| func InitDDLNotifier( | ||
| sctx sessionctx.Context, | ||
| store Store, | ||
| pollInterval time.Duration, | ||
| ) { | ||
| globalDDLNotifier = &ddlNotifier{ | ||
| ownedSCtx: sctx, | ||
| store: store, | ||
| handlers: make(map[HandlerID]SchemaChangeHandler), | ||
| pollInterval: pollInterval, | ||
| } | ||
| } | ||
|
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| // ResetDDLNotifier is used for testing only. | ||
| func ResetDDLNotifier() { globalDDLNotifier = nil } | ||
|
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| // StartDDLNotifier starts the global ddlNotifier. It will block until the | ||
| // context is canceled. | ||
| func StartDDLNotifier(ctx context.Context) { | ||
| globalDDLNotifier.Start(ctx) | ||
| } | ||
|
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| // Start starts the ddlNotifier. It will block until the context is canceled. | ||
| func (n *ddlNotifier) Start(ctx context.Context) { | ||
| ctx = kv.WithInternalSourceType(ctx, kv.InternalDDLNotifier) | ||
| ticker := time.NewTicker(n.pollInterval) | ||
| defer ticker.Stop() | ||
| for { | ||
| select { | ||
| case <-ctx.Done(): | ||
| return | ||
| case <-ticker.C: | ||
| if err := n.processEvents(ctx); err != nil { | ||
| logutil.Logger(ctx).Error("Error processing events", zap.Error(err)) | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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| func (n *ddlNotifier) processEvents(ctx context.Context) error { | ||
| changes, err := n.store.List(ctx, sess.NewSession(n.ownedSCtx)) | ||
| if err != nil { | ||
| return errors.Trace(err) | ||
| } | ||
|
|
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| // we should ensure deliver order of events to a handler, so if a handler returns | ||
| // error for previous events it should not receive later events. | ||
| skipHandlers := make(map[HandlerID]struct{}) | ||
| for _, change := range changes { | ||
| for handlerID, handler := range n.handlers { | ||
| if _, ok := skipHandlers[handlerID]; ok { | ||
| continue | ||
| } | ||
| if err2 := n.processEventForHandler(ctx, change, handlerID, handler); err2 != nil { | ||
| skipHandlers[handlerID] = struct{}{} | ||
|
|
||
| if !goerr.Is(err2, ErrNotReadyRetryLater) { | ||
| logutil.Logger(ctx).Error("Error processing change", | ||
| zap.Int64("ddlJobID", change.ddlJobID), | ||
| zap.Int64("multiSchemaChangeSeq", change.multiSchemaChangeSeq), | ||
| zap.Int("handlerID", int(handlerID)), | ||
| zap.Error(err2)) | ||
| } | ||
| continue | ||
| } | ||
| } | ||
| // TODO: remove the processed change after all handlers processed it. | ||
| } | ||
|
|
||
| return nil | ||
| } | ||
|
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| func (n *ddlNotifier) processEventForHandler( | ||
| ctx context.Context, | ||
| change *schemaChange, | ||
| handlerID HandlerID, | ||
| handler SchemaChangeHandler, | ||
| ) (err error) { | ||
| if (change.processedByFlag & (1 << handlerID)) != 0 { | ||
| return nil | ||
| } | ||
|
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| se := sess.NewSession(n.ownedSCtx) | ||
|
|
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| if err = se.Begin(ctx); err != nil { | ||
| return errors.Trace(err) | ||
| } | ||
| defer func() { | ||
| if err == nil { | ||
| err = errors.Trace(se.Commit(ctx)) | ||
| } else { | ||
| se.Rollback() | ||
| } | ||
| }() | ||
|
|
||
| // TODO: Should we attach a timeout to this ctx? | ||
| if err = handler(ctx, n.ownedSCtx, change.event); err != nil { | ||
| return errors.Trace(err) | ||
| } | ||
|
|
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| newFlag := change.processedByFlag | (1 << handlerID) | ||
| if err = n.store.UpdateProcessed( | ||
| ctx, | ||
| se, | ||
| change.ddlJobID, | ||
| change.multiSchemaChangeSeq, | ||
| newFlag, | ||
| ); err != nil { | ||
| return errors.Trace(err) | ||
| } | ||
| change.processedByFlag = newFlag | ||
|
|
||
| return nil | ||
| } |
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