README
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Database Connections
The dbconn package provides MySQL database connection management and locking utilities for Spirit. It wraps database/sql with Spirit-specific concerns: retry logic, TLS auto-configuration, advisory locking, table locking, and the ability to kill blocking transactions.
Connection Setup
When creating a new connection, Spirit appends standardized DSN parameters to ensure consistent behavior across all connections. These include setting sql_mode="" (to be able to copy legacy data like 0000-00-00), time_zone=+00:00, transaction_isolation=read-committed, charset=utf8mb4, collation=utf8mb4_bin, and rejectReadOnly=true (for Aurora failover resilience). This means that regardless of the server's global configuration, Spirit connections behave predictably.
TLS
Spirit supports five TLS modes: DISABLED, PREFERRED, REQUIRED, VERIFY_CA, and VERIFY_IDENTITY. The default is PREFERRED, which first attempts a TLS connection and falls back to plaintext if it fails. RDS hosts are auto-detected via hostname pattern matching (*.rds.amazonaws.com), and an embedded RDS CA bundle is used automatically.
Retryable Transactions
RetryableTransaction is the primary mechanism for executing statements that may encounter transient errors. It classifies MySQL errors into retryable (deadlocks, lock wait timeouts, connection loss, read-only mode, killed queries) and fatal (everything else). On transient errors, the entire transaction is retried up to MaxRetries times.
An important subtlety is that RetryableTransaction inspects SHOW WARNINGS after every statement. This catches issues that MySQL does not surface as errors, such as range_optimizer_max_mem_size exceeded warnings. This particular warning is treated as fatal because it indicates a table scan will occur instead of an index range scan.
Force Kill
Both ForceExec and NewTableLock implement a timer-based force-kill pattern. They wait for 90% of LockWaitTimeout, then query performance_schema to identify and kill transactions that are blocking metadata lock acquisition. This is enabled by default and can be disabled with Spirit's --skip-force-kill flag.
There are two important safety constraints:
- Transaction weight threshold: Transactions with a weight above 1,000,000 (as reported by
information_schema.innodb_trx.trx_weight) are never killed, because their rollback would be expensive and disruptive. - Explicit table locks: Connections holding
LOCK TABLESare never killed. Instead, anErrTableLockFounderror is returned. This is because killing non-transactional locks is unsafe.
Metadata Lock
MetadataLock provides an advisory locking mechanism using MySQL's GET_LOCK() function. It runs on a dedicated single-connection database pool with a background goroutine that periodically refreshes the lock. If the connection drops, it automatically reconnects and re-acquires locks.
Lock names are deterministic hashes of schema.table, truncated with a SHA1 suffix to fit MySQL's 64-character limit for lock names. This is used to prevent concurrent Spirit migrations on the same table.
Table Lock
TableLock wraps MySQL's LOCK TABLES ... WRITE statement. It integrates with the force-kill mechanism to automatically kill blocking transactions if the lock cannot be acquired within the timeout. This is used during the cutover phase.
Transaction Pool
TrxPool pre-creates a pool of REPEATABLE READ transactions with START TRANSACTION WITH CONSISTENT SNAPSHOT. This ensures all worker threads see the same point-in-time data, which is essential for parallel checksum verification.
See Also
- pkg/dbconn/sqlescape - Client-side SQL escaping
- pkg/checksum - Uses
TrxPoolfor consistent parallel checksumming - pkg/migration - Uses force-kill and metadata locks during schema changes
Documentation
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Overview ¶
Package dbconn contains a series of database-related utility functions.
Index ¶
- Constants
- Variables
- func BeginStandardTrx(ctx context.Context, db *sql.DB, opts *sql.TxOptions) (*sql.Tx, int, error)
- func EnhanceDSNWithTLS(inputDSN string, config *DBConfig) (string, error)
- func Exec(ctx context.Context, db *sql.DB, stmt string, args ...any) error
- func ForceExec(ctx context.Context, db *sql.DB, tables []*table.TableInfo, dbConfig *DBConfig, ...) error
- func GetEmbeddedRDSBundle() []byte
- func GetLockingTransactions(ctx context.Context, db *sql.DB, tables []*table.TableInfo, config *DBConfig, ...) ([]int, error)
- func GetTLSConfigForBinlog(config *DBConfig, host string) (*tls.Config, error)
- func IsRDSHost(host string) bool
- func KillLockingTransactions(ctx context.Context, db *sql.DB, tables []*table.TableInfo, config *DBConfig, ...) error
- func KillTransaction(ctx context.Context, db *sql.DB, pid int) error
- func LoadCertificateFromFile(filePath string) ([]byte, error)
- func New(inputDSN string, config *DBConfig) (db *sql.DB, err error)
- func NewCustomTLSConfig(certData []byte, sslMode string) *tls.Config
- func NewTLSConfig() *tls.Config
- func NewWithConnectionType(inputDSN string, config *DBConfig, connectionType string) (db *sql.DB, err error)
- func RetryableTransaction(ctx context.Context, db *sql.DB, ignoreDupKeyWarnings bool, config *DBConfig, ...) (int64, error)
- type DBConfig
- type LockDetail
- type MetadataLock
- type TableLock
- type TrxPool
Constants ¶
const ( // TableLockQuery is used to find tables that are locked by a LOCK TABLES command. // It's not really possible to find out how long the lock has been held, so we don't consider // the length of the lock here. TableLockQuery = `` /* 440-byte string literal not displayed */ LongRunningEventQuery = `` /* 751-byte string literal not displayed */ )
Variables ¶
var ( // TransactionWeightThreshold is the maximum information_schema.innodb_trx.trx_weight // over which we consider a transaction too big to be safely killed. Rolling back a // heavy transaction can cause a huge impact on the database. TransactionWeightThreshold int64 = 1_000_000 ErrTableLockFound = errors.New("explicit table lock found! spirit cannot proceed") )
Functions ¶
func BeginStandardTrx ¶
BeginStandardTrx is like db.BeginTx but returns the connection id.
func EnhanceDSNWithTLS ¶
EnhanceDSNWithTLS enhances a DSN with TLS settings from the provided config if the DSN doesn't already contain TLS parameters. This allows replica connections to inherit TLS settings from the main connection while still respecting explicit TLS configuration in the DSN.
func Exec ¶
Exec is like db.Exec but only returns an error. This makes it a little bit easier to use in error handling. It accepts args which are escaped client side using the TiDB escape library. i.e. %n is an identifier, %? is automatic type conversion on a variable.
func ForceExec ¶
func ForceExec(ctx context.Context, db *sql.DB, tables []*table.TableInfo, dbConfig *DBConfig, logger *slog.Logger, stmt string, args ...any) error
ForceExec is like Exec but it has some added logic to force kill any connections that are holding up metadata locks preventing this from succeeding.
func GetEmbeddedRDSBundle ¶
func GetEmbeddedRDSBundle() []byte
GetEmbeddedRDSBundle returns the embedded RDS certificate bundle
func GetLockingTransactions ¶
func GetLockingTransactions(ctx context.Context, db *sql.DB, tables []*table.TableInfo, config *DBConfig, logger *slog.Logger, ignorePIDs []int) ([]int, error)
GetLockingTransactions queries the performance schema to find locking transactions that are holding locks on the specified tables. It returns a list of PIDs of these transactions. If no tables are specified, it will return all long-running transactions. If a transaction's weight exceeds the TransactionWeightThreshold, it will be skipped. If no long-running transactions are found, it returns nil.
func GetTLSConfigForBinlog ¶
GetTLSConfigForBinlog creates a TLS config for binary log connections using the same logic as main database connections
func KillLockingTransactions ¶
func LoadCertificateFromFile ¶
LoadCertificateFromFile loads certificate data from a file
func New ¶
New is similar to sql.Open except we take the inputDSN and append additional options to it to standardize the connection. It will also ping the connection to ensure it is valid.
func NewCustomTLSConfig ¶
NewCustomTLSConfig creates a TLS config based on SSL mode and certificate data
func NewTLSConfig ¶
NewTLSConfig creates a TLS config using the embedded RDS global bundle
func NewWithConnectionType ¶
func NewWithConnectionType(inputDSN string, config *DBConfig, connectionType string) (db *sql.DB, err error)
NewWithConnectionType is like New but includes context about the connection type for better error messages
func RetryableTransaction ¶
func RetryableTransaction(ctx context.Context, db *sql.DB, ignoreDupKeyWarnings bool, config *DBConfig, stmts ...string) (int64, error)
RetryableTransaction retries all statements in a transaction, retrying if a statement errors, or there is a deadlock. It will retry up to maxRetries times.
Types ¶
type DBConfig ¶
type DBConfig struct {
LockWaitTimeout int
InnodbLockWaitTimeout int
MaxRetries int
MaxOpenConnections int
RangeOptimizerMaxMemSize int64
InterpolateParams bool
ForceKill bool // If true, kill locking transactions to acquire metadata locks (default: true)
// TLS Configuration
TLSMode string // TLS connection mode (DISABLED, PREFERRED, REQUIRED, VERIFY_CA, VERIFY_IDENTITY)
TLSCertificatePath string // Path to custom TLS certificate file
}
func NewDBConfig ¶
func NewDBConfig() *DBConfig
type LockDetail ¶
type LockDetail struct {
PID int
User sql.NullString
Host sql.NullString
Info sql.NullString
ObjectType sql.NullString
ObjectSchema sql.NullString
ObjectName sql.NullString
LockType sql.NullString // e.g. "INTENTION_EXCLUSIVE", "SHARED_READ",
LockDuration sql.NullString // e.g. "STATEMENT", "TRANSACTION"
LockStatus sql.NullString
RunningTime sql.NullString // Human-readable format of the timer_wait
TimerWait sql.NullInt64 // in picoseconds
TrxWeight sql.NullInt64 // Rows modified by the transaction
}
type MetadataLock ¶
type MetadataLock struct {
// contains filtered or unexported fields
}
func NewMetadataLock ¶
func (*MetadataLock) Close ¶
func (m *MetadataLock) Close() error
func (*MetadataLock) CloseDBConnection ¶
func (m *MetadataLock) CloseDBConnection(logger *slog.Logger) error
type TableLock ¶
type TableLock struct {
// contains filtered or unexported fields
}
func NewTableLock ¶
func NewTableLock(ctx context.Context, db *sql.DB, tables []*table.TableInfo, config *DBConfig, logger *slog.Logger) (*TableLock, error)
NewTableLock creates a new server wide lock on multiple tables. i.e. LOCK TABLES .. WRITE. It uses a short timeout and *does not retry*. The caller is expected to retry, which gives it a chance to first do things like catch up on replication apply before it does the next attempt.
config.ForceKill=true is the default, and will more or less ensure that the lock acquisition is successful by killing long-running queries that are blocking our lock acquisition after we have waited for 90% of our configured LockWaitTimeout. It can be disabled with --skip-force-kill.
Source Files
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