Merge pull request #8644 from Roasbeef/remove-sql-mutex-part-deux

kvdb/postgres: remove global application level lock

Author: Roasbeef

kvdb/postgres/db.go

@@ -28,7 +28,6 @@ func newPostgresBackend(ctx context.Context, config *Config, prefix string) (
 		Schema:                "public",
 		TableNamePrefix:       prefix,
 		SQLiteCmdReplacements: sqliteCmdReplacements,
-		WithTxLevelLock:       true,
 	}
 
 	return sqlbase.NewSqlBackend(ctx, cfg)

kvdb/sqlbase/db.go

@@ -55,10 +55,6 @@ type Config struct {
 	// commands. Note that the sqlite keywords to be replaced are
 	// case-sensitive.
 	SQLiteCmdReplacements SQLiteCmdReplacements
-
-	// WithTxLevelLock when set will ensure that there is a transaction
-	// level lock.
-	WithTxLevelLock bool
 }
 
 // db holds a reference to the sql db connection.
@@ -79,10 +75,6 @@ type db struct {
 	// db is the underlying database connection instance.
 	db *sql.DB
 
-	// lock is the global write lock that ensures single writer. This is
-	// only used if cfg.WithTxLevelLock is set.
-	lock sync.RWMutex
-
 	// table is the name of the table that contains the data for all
 	// top-level buckets that have keys that cannot be mapped to a distinct
 	// sql table.

kvdb/sqlbase/readwrite_tx.go

@@ -5,7 +5,6 @@ package sqlbase
 import (
 	"context"
 	"database/sql"
-	"sync"
 
 	"github.com/btcsuite/btcwallet/walletdb"
 )
@@ -20,28 +19,11 @@ type readWriteTx struct {
 
 	// active is true if the transaction hasn't been committed yet.
 	active bool
-
-	// locker is a pointer to the global db lock.
-	locker sync.Locker
 }
 
 // newReadWriteTx creates an rw transaction using a connection from the
 // specified pool.
 func newReadWriteTx(db *db, readOnly bool) (*readWriteTx, error) {
-	locker := newNoopLocker()
-	if db.cfg.WithTxLevelLock {
-		// Obtain the global lock instance. An alternative here is to
-		// obtain a database lock from Postgres. Unfortunately there is
-		// no database-level lock in Postgres, meaning that each table
-		// would need to be locked individually. Perhaps an advisory
-		// lock could perform this function too.
-		locker = &db.lock
-		if readOnly {
-			locker = db.lock.RLocker()
-		}
-	}
-	locker.Lock()
-
 	// Start the transaction. Don't use the timeout context because it would
 	// be applied to the transaction as a whole. If possible, mark the
 	// transaction as read-only to make sure that potential programming
@@ -54,15 +36,13 @@ func newReadWriteTx(db *db, readOnly bool) (*readWriteTx, error) {
 		},
 	)
 	if err != nil {
-		locker.Unlock()
 		return nil, err
 	}
 
 	return &readWriteTx{
 		db:     db,
 		tx:     tx,
 		active: true,
-		locker: locker,
 	}, nil
 }
 
@@ -94,7 +74,6 @@ func (tx *readWriteTx) Rollback() error {
 
 	// Unlock the transaction regardless of the error result.
 	tx.active = false
-	tx.locker.Unlock()
 	return err
 }
 
@@ -162,7 +141,6 @@ func (tx *readWriteTx) Commit() error {
 
 	// Unlock the transaction regardless of the error result.
 	tx.active = false
-	tx.locker.Unlock()
 
 	return err
 }
@@ -204,25 +182,3 @@ func (tx *readWriteTx) Exec(query string, args ...interface{}) (sql.Result,
 
 	return tx.tx.ExecContext(ctx, query, args...)
 }
-
-// noopLocker is an implementation of a no-op sync.Locker.
-type noopLocker struct{}
-
-// newNoopLocker creates a new noopLocker.
-func newNoopLocker() sync.Locker {
-	return &noopLocker{}
-}
-
-// Lock is a noop.
-//
-// NOTE: this is part of the sync.Locker interface.
-func (n *noopLocker) Lock() {
-}
-
-// Unlock is a noop.
-//
-// NOTE: this is part of the sync.Locker interface.
-func (n *noopLocker) Unlock() {
-}
-
-var _ sync.Locker = (*noopLocker)(nil)