127 lines
2.8 KiB
Go
127 lines
2.8 KiB
Go
package cassandra
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import (
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"context"
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"fmt"
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"time"
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"github.com/scylladb/gocqlx/v3/qb"
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)
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const (
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defaultTTLSec = 30
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defaultRetry = 3
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baseDelay = 100 * time.Millisecond
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)
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// LockOption 用來設定 TryLock 的 TTL 行為
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type LockOption func(*lockOptions)
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type lockOptions struct {
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ttlSeconds int // TTL，單位秒；<=0 代表不 expire
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}
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func WithLockTTL(d time.Duration) LockOption {
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return func(o *lockOptions) {
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o.ttlSeconds = int(d.Seconds())
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}
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}
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// WithNoLockExpire 永不自動解鎖
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func WithNoLockExpire() LockOption {
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return func(o *lockOptions) {
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o.ttlSeconds = 0
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}
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}
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// TryLock 嘗試在表上插入一筆唯一鍵（IF NOT EXISTS）作為鎖
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// 預設 30 秒 TTL，可透過 option 調整或取消 TTL
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func (db *CassandraDB) TryLock(
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ctx context.Context,
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document any,
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keyspace string,
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opts ...LockOption,
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) error {
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// 1. 解析 metadata
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metadata, err := GenerateTableMetadata(document, keyspace)
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if err != nil {
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return err
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}
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// 2. 組合 option
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options := &lockOptions{ttlSeconds: defaultTTLSec}
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for _, opt := range opts {
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opt(options)
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}
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// 3. 建 TTL 子句
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builder := qb.Insert(metadata.Name).
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Unique(). // IF NOT EXISTS
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Columns(metadata.Columns...)
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if options.ttlSeconds > 0 {
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ttl := time.Duration(options.ttlSeconds) * time.Second
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builder = builder.TTL(ttl)
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}
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stmt, names := builder.ToCql()
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// 4. 執行 CAS
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q := db.GetSession().Query(stmt, names).BindStruct(document).
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WithContext(ctx).
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WithTimestamp(time.Now().UnixNano() / 1e3)
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applied, err := q.ExecCASRelease()
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if err != nil {
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return err
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}
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if !applied {
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return fmt.Errorf("failed to acquire lock")
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}
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return nil
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}
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// UnLock 砍掉鎖，其實就是 Delete
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func (db *CassandraDB) UnLock(ctx context.Context, filter any, keyspace string) error {
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if filter == nil {
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return fmt.Errorf("unlock failed: nil filter")
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}
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metadata, err := GenerateTableMetadata(filter, keyspace)
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if err != nil {
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return fmt.Errorf("unlock: generate metadata failed: %w", err)
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}
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if len(metadata.Columns) == 0 {
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return fmt.Errorf("unlock failed: missing primary key in struct")
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}
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var lastErr error
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for i := 0; i < defaultRetry; i++ {
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builder := qb.Delete(metadata.Name).Existing()
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// 動態添加 WHERE 條件
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for _, key := range metadata.PartKey {
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builder = builder.Where(qb.Eq(key))
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}
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stmt, names := builder.ToCql()
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q := db.GetSession().Query(stmt, names).BindStruct(filter).
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WithContext(ctx).
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WithTimestamp(time.Now().UnixNano() / 1e3)
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applied, err := q.ExecCASRelease()
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if err == nil && applied {
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return nil
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}
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if err != nil {
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lastErr = fmt.Errorf("unlock error: %w", err)
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} else if !applied {
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lastErr = fmt.Errorf("unlock not applied: row not found or not visible yet")
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}
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time.Sleep(baseDelay * time.Duration(1<<i)) // 100ms → 200ms → 400ms
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}
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return fmt.Errorf("unlock failed after retries: %w", lastErr)
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}
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