X sqlite: Switch to using github.com/gwenn/gosqlite directly

go/neo/storage/sqlite/pool.go

+// Copyright (C) 2018  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package sqlite
+// simple connection pool
+
+import (
+	"errors"
+	"sync"
+
+	"lab.nexedi.com/kirr/go123/xerr"
+
+	sqlite3 "github.com/gwenn/gosqlite"
+)
+
+// connPool is a pool of sqlite3.Conn
+type connPool struct {
+	factory func() (*sqlite3.Conn, error) // =nil if pool closed
+
+	mu     sync.Mutex
+	connv  []*sqlite3.Conn // operated as stack
+}
+
+// newConnPool creates new connPool that will be using factory to create new
+// connections.
+func newConnPool(factory func() (*sqlite3.Conn, error)) *connPool {
+	return &connPool{factory: factory}
+}
+
+// Close closes pool and all connections that were in it.
+func (p *connPool) Close() error {
+	p.mu.Lock()
+	connv := p.connv
+	p.connv = nil
+	p.factory = nil
+	p.mu.Unlock()
+
+	var errv xerr.Errorv
+	for _, conn := range connv {
+		err := conn.Close()
+		errv.Appendif(err)
+	}
+
+	return errv.Err()
+}
+
+var errClosedPool = errors.New("sqlite: pool: getConn on closed pool")
+
+// getConn returns a connection - either from pool, or newly created if the
+// pool was empty.
+func (p *connPool) getConn() (conn *sqlite3.Conn, _ error) {
+	p.mu.Lock()
+
+	factory := p.factory
+	if factory == nil {
+		p.mu.Unlock()
+		return nil, errClosedPool
+	}
+
+	if l := len(p.connv); l > 0 {
+		l--
+		conn = p.connv[l]
+		p.connv[l] = nil  // just in case
+		p.connv = p.connv[:l]
+	}
+
+	p.mu.Unlock()
+
+	if conn != nil {
+		return conn, nil
+	}
+
+	// pool was empty - we need to create new connection
+	return factory()
+}
+
+// putConn puts a connection to pool.
+//
+// Caller must not directly use conn after call to putConn anymore.
+func (p *connPool) putConn(conn *sqlite3.Conn) {
+	p.mu.Lock()
+	if p.factory != nil { // forgiving putConn after close
+		p.connv = append(p.connv, conn)
+	}
+	p.mu.Unlock()
+}

go/neo/storage/sqlite/sqlite.go

 // Copyright (C) 2018  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//                     schema & queries are based on neo/storage/database/sqlite.py
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
 // it under the terms of the GNU General Public License version 3, or (at your
@@ -21,9 +23,11 @@ package sqlite
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net/url"
-	"reflect"
+	"strings"
+	//"reflect"
 
 	"lab.nexedi.com/kirr/go123/mem"
 	"lab.nexedi.com/kirr/go123/xerr"
@@ -32,8 +36,34 @@ import (
 	"lab.nexedi.com/kirr/neo/go/neo/storage"
 	"lab.nexedi.com/kirr/neo/go/zodb"
 
-	"database/sql"
-        _ "github.com/mattn/go-sqlite3"
+	// NOTE github.com/gwenn/gosqlite is used for the following reasons:
+	//
+	// - it is used directly instead of using it via "database/sql" because for a
+	//   typical 5µs query quering through "database/sql", even in the most
+	//   careful, hacky and unsafe way, adds at least 3µs and more.
+	//   see also: https://github.com/golang/go/issues/23879
+	//
+	// - "github.com/mattn/go-sqlite3" does not provide a good way to Scan
+	//   queries made directly.
+	//
+	// we need to do only simple queries and thus do not use any Cgo->Go
+	// callback-related functionality from github.com/gwenn/gosqlite. This
+	// way it should be safe for us to use it even without GODEBUG=cgocheck=0.
+	//
+	// --------
+	//
+	// NOTE 2: we do not interrupt requests on context cancelation:
+	//
+	// - it is relatively expensive to support when using a CGo library - see e.g.
+	//   https://github.com/mattn/go-sqlite3/pull/530
+	//   https://github.com/golang/go/issues/19574#issuecomment-366513872
+	//
+	// - on Linux disk file IO, in contrast to e.g. network and pipes,
+	//   cannot be really interrupted.
+	//
+	// so we are ok for the cancel to be working on the granualarity of
+	// whole query.
+	sqlite3 "github.com/gwenn/gosqlite"
 )
 
 // ---- schema ----
@@ -132,30 +162,115 @@ const tobj = `
 
 
 type Backend struct {
-	db  *sql.DB
+	pool *connPool
 	url  string
 }
 
 var _ storage.Backend = (*Backend)(nil)
 
-func (b *Backend) query1(ctx context.Context, query string, argv ...interface{}) *sql.Row {
-	return b.db.QueryRowContext(ctx, query, argv...)
+// row1 is like sql.Row to Scan values once and then put stmt and conn back to their pools.
+type row1 struct {
+	pool *connPool
+	conn *sqlite3.Conn
+	stmt *sqlite3.Stmt
+	err  error		// != nil on an error obtaining the row
 }
 
+var errNoRows = errors.New("sqlite: no rows in result set")
+
+func (r *row1) Scan(argv ...interface{}) error {
+	if r.pool == nil {
+		panic("sqlite: row1: .Scan called second time")
+	}
+
+	err := r.err
+	if err == nil {
+		err = r.stmt.Scan(argv...)
+	}
+
+	if r.stmt != nil {
+		err2 := r.stmt.Reset() // else it won't be put back to cache
+		if err == nil {
+			err = err2
+		}
+
+		err2 = r.stmt.Finalize() // -> conn's stmt cache
+		if err == nil {
+			err = err2
+		}
+
+		r.stmt = nil // just in case
+	}
+
+	if r.conn != nil {
+		r.pool.putConn(r.conn)
+		r.conn = nil
+	}
+
+	// to catch double .Scan
+	r.pool = nil
+
+	return err
+}
+
+// query1 performs 1 select-like query.
+//
+// the result needs to be .Scan'ned once similarly to how it is done in database/sql.
+func (b *Backend) query1(query string, argv ...interface{}) *row1 {
+	row := &row1{pool: b.pool}
+
+	// pool -> conn
+	conn, err := b.pool.getConn()
+	if err != nil {
+		row.err = err
+		return row
+	}
+	row.conn = conn
+
+	// conn -> stmt
+	stmt, err := conn.Prepare(query) // uses conn's stmt cache
+	if err != nil {
+		row.err = err
+		return row
+	}
+	row.stmt = stmt
+
+	// stmt += argv
+	err = stmt.Bind(argv...)
+	if err != nil {
+		row.err = err
+		return row
+	}
+
+	// everything prepared - run the query
+	ok, err := stmt.Next()
+	if err != nil {
+		row.err = err
+		return row
+	}
+
+	if !ok {
+		row.err = errNoRows
+	}
+
+	return row
+}
+
+
+
 func (b *Backend) LastTid(ctx context.Context) (zodb.Tid, error) {
 	var lastTid zodb.Tid
 
 	// FIXME nodeID <- my node UUID
 	myID := proto.UUID(proto.STORAGE, 1)
 
-	err := b.query1(ctx,
-		"SELECT MAX(tid) FROM pt, trans" +
+	err := b.query1("SELECT MAX(tid) FROM pt, trans" +
 			" WHERE nid=? AND rid=partition" /* XXX AND tid<=? (max_tid) */,
 			myID).Scan(&lastTid)
 
 	if err != nil {
 		// no transaction have been committed
-		if err == sql.ErrNoRows {
+		if err == errNoRows {
 			return 0, nil
 		}
 
@@ -171,13 +286,12 @@ func (b *Backend) LastOid(ctx context.Context) (zodb.Oid, error) {
 	// FIXME nodeID <- my node UUID
 	myID := proto.UUID(proto.STORAGE, 1)
 
-	err := b.query1(ctx,
-		"SELECT MAX(oid) FROM pt, obj WHERE nid=? AND rid=partition",
+	err := b.query1("SELECT MAX(oid) FROM pt, obj WHERE nid=? AND rid=partition",
 			myID).Scan(&lastOid)
 
 	if err != nil {
 		// no objects
-		if err == sql.ErrNoRows {
+		if err == errNoRows {
 			return proto.INVALID_OID, nil
 		}
 
@@ -199,12 +313,14 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 	//var data sql.RawBytes
 	var data []byte
 
+	// XXX recheck vvv with sqlite3 direct
 	// hash is variable-length BLOB - Scan refuses to put it into [20]byte
 	//var hash sql.RawBytes
 	var hash []byte
 
 	// obj.value_tid can be null
-	var valueTid sql.NullInt64	// XXX ok not to uint64 - max tid is max signed int64
+	//var valueTid sql.NullInt64	// XXX ok not to uint64 - max tid is max signed int64
+	var valueTid int64	// XXX ok not to uint64 - max tid is max signed int64
 
 	// FIXME pid = getReadablePartition (= oid % Np; error if pid not readable)
 	pid := 0
@@ -212,7 +328,9 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 	// XXX somehow detect errors in sql misuse and log them as 500 without reporting to client?
 	// XXX such errors start with "unsupported Scan, "
 
-	err = b.query1(ctx,
+	// XXX use conn for severl query1 (see below) without intermediate returns to pool?
+
+	err = b.query1(
 		"SELECT tid, compression, data.hash, value, value_tid" +
 		" FROM obj LEFT JOIN data ON obj.data_id = data.id" +
 		" WHERE partition=? AND oid=? AND tid<=?" +
@@ -221,10 +339,10 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 		Scan(&obj.Serial, &obj.Compression, &hash, &data, &valueTid)
 
 	if err != nil {
-		if err == sql.ErrNoRows {
+		if err == errNoRows {
 			// nothing found - check whether object exists at all
 			var __ zodb.Oid
-			err = b.query1(ctx,
+			err = b.query1(
 				"SELECT oid FROM obj WHERE partition=? AND oid=? LIMIT 1",
 				pid, xid.Oid) .Scan(&__)
 
@@ -235,7 +353,7 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 					DeletedAt: 0,		// XXX hardcoded
 				}
 
-			case err == sql.ErrNoRows:
+			case err == errNoRows:
 				err = &zodb.NoObjectError{Oid: xid.Oid}
 
 			}
@@ -251,8 +369,8 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 	copy(obj.Checksum[:], hash)
 
 	// valueTid -> obj.DataSerial
-	if valueTid.Valid {
-		obj.DataSerial = zodb.Tid(valueTid.Int64)
+	if valueTid != 0 {
+		obj.DataSerial = zodb.Tid(valueTid)
 	}
 
 
@@ -262,7 +380,7 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 
 	// find out nextSerial
 	// XXX kill nextSerial support after neo/py cache does not need it
-	err = b.query1(ctx,
+	err = b.query1(
 		"SELECT tid from obj" +
 		" WHERE partition=? AND oid=? AND tid>?" +
 		" ORDER BY tid LIMIT 1",
@@ -270,7 +388,7 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 		Scan(&obj.NextSerial)
 
 	if err != nil {
-		if err == sql.ErrNoRows {
+		if err == errNoRows {
 			obj.NextSerial = proto.INVALID_TID
 		} else {
 			return nil, err
@@ -281,51 +399,59 @@ func (b *Backend) Load(ctx context.Context, xid zodb.Xid) (_ *proto.AnswerObject
 }
 
 
-func (b *Backend) config(ctx context.Context, key string, pvalue interface{}) error {
-	return b.query1(ctx, "SELECT value FROM config WHERE name=?", key).Scan(pvalue)
+func (b *Backend) config(key string, pvalue *string) error {
+	return b.query1("SELECT value FROM config WHERE name=?", key).Scan(pvalue)
+}
+
+func (b *Backend) Close() error {
+	err := b.pool.Close()
+	return err	// XXX err ctx
 }
 
 // ---- open by URL ----
 
 func openURL(ctx context.Context, u *url.URL) (_ storage.Backend, err error) {
-	// TODO handle query
-	// XXX u.Path is not always raw path - recheck and fix
-	path := u.Host + u.Path
-
-	db, err := sql.Open("sqlite3", path)
-	if err != nil {
-		return nil, err
+	url := u.String()
+	dburl := strings.TrimPrefix(url, u.Scheme+"://") // url with stripped sqlite://
+	connFactory := func() (*sqlite3.Conn, error) {
+		return sqlite3.Open(dburl)
 	}
 
-	b := &Backend{db: db, url: u.String()}
+	b := &Backend{pool: newConnPool(connFactory), url: url}
 
 	defer func() {
 		if err != nil {
-			db.Close()
+			b.Close()
 		}
 	}()
 
 	// check we can actually access db
-	err = db.PingContext(ctx)
+	conn, err := b.pool.getConn()
+	if err == nil {
+		err = conn.Close()
+	}
 	if err != nil {
-		return nil, err	// XXX err ctx
+		return nil, err
 	}
 
 	// check schema and that our limited version can work with the db
+	// (by making some queries in open we also check whether we can access db at all)
 	errv := xerr.Errorv{}
 	checkConfig := func(name string, expect interface{}) {
-		pvalue := reflect.New(reflect.TypeOf(expect)).Interface()
-		err := b.config(ctx, name, pvalue)
+		//pvalue := reflect.New(reflect.TypeOf(expect)).Interface()
+		value := ""
+		err := b.config(name, &value)
 
 		// XXX prefix "b.path: config: %s:"
 
 		switch err {
-		case sql.ErrNoRows:
+		case errNoRows:
 			err = fmt.Errorf("not found")
 		case nil:
-			value := reflect.ValueOf(pvalue).Elem().Interface()
-			if value != expect {
-				err = fmt.Errorf("got %v; want %v", value, expect)
+			//value := reflect.ValueOf(pvalue).Elem().Interface()
+			sexpect := fmt.Sprintf("%v", expect)
+			if value != sexpect {
+				err = fmt.Errorf("got %v; want %v", value, sexpect)
 			}
 		}
 
@@ -335,7 +461,7 @@ func openURL(ctx context.Context, u *url.URL) (_ storage.Backend, err error) {
 	}
 
 	checkConfig("version",		schemaVersion)
-	checkConfig("nid",		proto.UUID(proto.STORAGE, 1))
+	checkConfig("nid",		int(proto.UUID(proto.STORAGE, 1)))
 	checkConfig("partitions",	1)
 	checkConfig("replicas",		1)
 
@@ -358,8 +484,8 @@ func openURL(ctx context.Context, u *url.URL) (_ storage.Backend, err error) {
 	// not-yet-moved to trans/tobj transactions.
 	nttrans, ntobj := 0, 0
 	errv = xerr.Errorv{}
-	errv.Appendif( b.query1(ctx, "SELECT COUNT(*) FROM ttrans") .Scan(&nttrans) )
-	errv.Appendif( b.query1(ctx, "SELECT COUNT(*) FROM tobj")   .Scan(&ntobj) )
+	errv.Appendif( b.query1("SELECT COUNT(*) FROM ttrans") .Scan(&nttrans) )
+	errv.Appendif( b.query1("SELECT COUNT(*) FROM tobj")   .Scan(&ntobj) )
 
 	err = errv.Err()
 	if err != nil {