- 数据请求阶段 -
Part 1 - 简单查询
1. 客户端发送 Query (‘Q’) 消息给服务端，包含了一条字符串类型的 SQL 语句。
func (cn *conn) query(query string, args []driver.Value) (_ *rows, err error) {\
...\
// Check to see if we can use the "simpleQuery" interface, which is\
// *much* faster than going through prepare/exec\
if len(args) == 0 {\
return cn.simpleQuery(query)\
}\
...\
}
2. 服务端收到 Query 消息，解析 SQL 语句，生成抽象语法树 (AST)，并传给执行器执行，获得结果。
func (c *conn) writeRowDescription(\
ctx context.Context,\
columns []sqlbase.ResultColumn,\
formatCodes []pgwirebase.FormatCode,\
w io.Writer,\
) error {\
c.msgBuilder.initMsg(pgwirebase.ServerMsgRowDescription)\
c.msgBuilder.putInt16(int16(len(columns)))\
for i, column := range columns {\
...\
c.msgBuilder.writeTerminatedString(column.Name)\
...\
c.msgBuilder.putInt32(0) // Table OID (optional).\
c.msgBuilder.putInt16(0) // Column attribute ID (optional).\
c.msgBuilder.putInt32(int32(typ.oid))\
c.msgBuilder.putInt16(int16(typ.size))\
...\
}\
...\
}
3. 服务端根据 SQL 结果，首先发送 RowDescription(B:‘T’) 消息，包含列的数量，列名，列的类型等参数。
func (c *conn) writeRowDescription(\
ctx context.Context,\
columns []sqlbase.ResultColumn,\
formatCodes []pgwirebase.FormatCode,\
w io.Writer,\
) error {\
c.msgBuilder.initMsg(pgwirebase.ServerMsgRowDescription)\
c.msgBuilder.putInt16(int16(len(columns)))\
for i, column := range columns {\
...\
c.msgBuilder.writeTerminatedString(column.Name)\
...\
c.msgBuilder.putInt32(0) // Table OID (optional).\
c.msgBuilder.putInt16(0) // Column attribute ID (optional).\
c.msgBuilder.putInt32(int32(typ.oid))\
c.msgBuilder.putInt16(int16(typ.size))\
...\
}\
...\
}
- RowDescription 消息后面将跟着多个 DataRow(B:‘D’) 消息，每个 DataRow 消息包含一行的数据。
func (c *conn) bufferRow(\
ctx context.Context,\
row tree.Datums,\
formatCodes []pgwirebase.FormatCode,\
conv sessiondata.DataConversionConfig,\
types []*types.T,\
) {\
c.msgBuilder.initMsg(pgwirebase.ServerMsgDataRow)\
c.msgBuilder.putInt16(int16(len(row)))\
for i, col := range row {\
...\
switch fmtCode {\
case pgwirebase.FormatText:\
c.msgBuilder.writeTextDatum(ctx, col, conv, types[i])\
case pgwirebase.FormatBinary:\
c.msgBuilder.writeBinaryDatum(ctx, col, conv.Location, types[i])\
...\
}\
if err := c.msgBuilder.finishMsg(&c.writerState.buf); err != nil {\
panic(fmt.Sprintf("unexpected err from buffer: %s", err))\
}\
}
5. 发送 CommandComplete(B:‘C’) 消息表示这个 SQL 请求执行结束了。
6. 服务端发送 ReadyForQuery(‘Z’)，通知客户端可以发送下一条 SQL 请求了。
func (r *commandResult) Close(ctx context.Context, t sql.TransactionStatusIndicator) {\
...\
switch r.typ {\
case commandComplete:\
tag := cookTag(\
r.cmdCompleteTag, r.conn.writerState.tagBuf[:0], r.stmtType, r.rowsAffected,\
)\
r.conn.bufferCommandComplete(tag)\
case parseComplete:\
r.conn.bufferParseComplete()\
case bindComplete:\
r.conn.bufferBindComplete()\
case closeComplete:\
r.conn.bufferCloseComplete()\
case readyForQuery:\
r.conn.bufferReadyForQuery(byte(t))\
// The error is saved on conn.err.\
_ /* err */ = r.conn.Flush(r.pos)\
...\
}\
...\
}
7. 客户端根据接受 SQL 请求的结果。
func (cn *conn) simpleQuery(q string) (res *rows, err error) {\
b := cn.writeBuf('Q')\
b.string(q)\
cn.send(b)\
\
for {\
t, r := cn.recv1()\
switch t {\
case 'C', 'I':\
...\
case 'Z':\
...\
case 'E':\
...\
case 'D':\
...\
case 'T':\
...\
}\
}\
}
Part 2 - 扩展查询
1. 客户端发送扩展查询请求，依次发送 Parse (F:‘P’), Bind (F:‘B’), Describe (F:‘D’), Execute (F:‘E’), Sync(F:‘S’) 消息。
func (cn *conn) query(query string, args []driver.Value) (_ *rows, err error) {\
...\
if cn.binaryParameters {\
cn.sendBinaryModeQuery(query, args)\
cn.readParseResponse()\
cn.readBindResponse()\
rows := &rows{cn: cn}\
rows.rowsHeader = cn.readPortalDescribeResponse()\
cn.postExecuteWorkaround()\
return rows, nil\
}\
...\
}
func (cn *conn) sendBinaryModeQuery(query string, args []driver.Value) {\
b := cn.writeBuf('P')\
b.byte(0) // unnamed statement\
b.string(query)\
b.int16(0)\
\
b.next('B')\
b.int16(0) // unnamed portal and statement\
cn.sendBinaryParameters(b, args)\
b.bytes(colFmtDataAllText)\
\
b.next('D')\
b.byte('P')\
b.byte(0) // unnamed portal\
\
b.next('E')\
b.byte(0)\
b.int32(0)\
\
b.next('S')\
cn.send(b)\
}
2. 服务端处理扩展查询请求。
3. 服务端发送回应消息，ParseComplete (B:‘1’), BindComplete (B:‘2’), ParameterDescription(B:‘t’), CommandComplete (B:‘C’), CloseComplete (B:‘3’), ReadyForQuery (B:‘Z’)。
func (r *commandResult) Close(ctx context.Context, t sql.TransactionStatusIndicator) {\
...\
switch r.typ {\
case commandComplete:\
tag := cookTag(\
r.cmdCompleteTag, r.conn.writerState.tagBuf[:0], r.stmtType, r.rowsAffected,\
)\
r.conn.bufferCommandComplete(tag)\
case parseComplete:\
r.conn.bufferParseComplete()\
case bindComplete:\
r.conn.bufferBindComplete()\
case closeComplete:\
r.conn.bufferCloseComplete()\
case readyForQuery:\
r.conn.bufferReadyForQuery(byte(t))\
// The error is saved on conn.err.\
_ /* err */ = r.conn.Flush(r.pos)\
...\
}\
...\
}
