MyCat 学习笔记 第二十一篇 . mycat 源代码分析 中

忍不住还是吐槽一下CSDN的编辑器,相同的内容是已经写第二次了。前一次都快写完,不小心再修改另一篇blog的内容,临时文章被冲掉了,真是哭死,CSDN还我2小时~~~

上一篇看了Mycat的启动与前端请求的处理,我们继续看看下报文 的响应与返回。

io.mycat.net.NIOSocketWR 做为前后端数据读写的实际操作类,在得到MySQL数据器反馈数据后会调用asynRead()方法,申请本次操作的所需要的buffer。

@Override
    public void asynRead() throws IOException {
        ByteBuffer theBuffer = con.readBuffer;
        if (theBuffer == null) {
            theBuffer = con.processor.getBufferPool().allocate();
            con.readBuffer = theBuffer;
        }
        int got = channel.read(theBuffer);
        con.onReadData(got);
    }

其中io.mycat.net. AbstractConnection作为所有数据库链接的抽象父类,已经实现了onReadData()方法,用来从socketChannel中读取二进制字节流。循环加载数据后即调用指定的handle方法分析、拆解报文 。

public void onReadData(int got) throws IOException {
//……
if (position >= offset + length && readBuffer != null) {

                // handle this package
                readBuffer.position(offset);                
                byte[] data = new byte[length];
                readBuffer.get(data, 0, length);
                handle(data);

                // maybe handle stmt_close
                if(isClosed()) {
                    return ;
                }

                // offset to next position
                offset += length;

                // reached end
                if (position == offset) {
                    // if cur buffer is temper none direct byte buffer and not
                    // received large message in recent 30 seconds
                    // then change to direct buffer for performance
                    if (readBuffer != null && !readBuffer.isDirect()
                            && lastLargeMessageTime < lastReadTime - 30 * 1000L) {  // used temp heap
                        if (LOGGER.isDebugEnabled()) {
                            LOGGER.debug("change to direct con read buffer ,cur temp buf size :" + readBuffer.capacity());
                        }
                        recycle(readBuffer);
                        readBuffer = processor.getBufferPool().allocateConReadBuffer();
                    } else {
                        if (readBuffer != null)
                            readBuffer.clear();
                    }
                    // no more data ,break
                    readBufferOffset = 0;
                    break;

// ……

@Override
    public void handle(byte[] data) {
        if (isSupportCompress()) {
            List<byte[]> packs = CompressUtil.decompressMysqlPacket(data, decompressUnfinishedDataQueue);
            for (byte[] pack : packs) {
                if (pack.length != 0)
                    handler.handle(pack);
            }
        } else {
            handler.handle(data);
        }
    }

由于是MySQL后端反回的数据,因此我们这里用得是 io.mycat.backend.mysql.nio. MySQLConnectionHandler
MySQLConnectionHandler的 handleData(byte[] data) 方法是具体的处理入口。
MyCat 学习笔记 第二十一篇 . mycat 源代码分析 中_第1张图片

@Override
    protected void handleData(byte[] data) {
        switch (resultStatus) {
        case RESULT_STATUS_INIT:
            switch (data[4]) {
            case OkPacket.FIELD_COUNT:
                handleOkPacket(data);
                break;
            case ErrorPacket.FIELD_COUNT:
                handleErrorPacket(data);
                break;
            case RequestFilePacket.FIELD_COUNT:
                handleRequestPacket(data);
                break;
            default:
                resultStatus = RESULT_STATUS_HEADER;
                header = data;
                fields = new ArrayList<byte[]>((int) ByteUtil.readLength(data,
                        4));
            }
            break;
        case RESULT_STATUS_HEADER:
            switch (data[4]) {
            case ErrorPacket.FIELD_COUNT:
                resultStatus = RESULT_STATUS_INIT;
                handleErrorPacket(data);
                break;
            case EOFPacket.FIELD_COUNT:
                resultStatus = RESULT_STATUS_FIELD_EOF;
                handleFieldEofPacket(data);
                break;
            default:
                fields.add(data);
            }
            break;
        case RESULT_STATUS_FIELD_EOF:
            switch (data[4]) {
            case ErrorPacket.FIELD_COUNT:
                resultStatus = RESULT_STATUS_INIT;
                handleErrorPacket(data);
                break;
            case EOFPacket.FIELD_COUNT:
                resultStatus = RESULT_STATUS_INIT;
                handleRowEofPacket(data);
                break;
            default:
                handleRowPacket(data);
            }
            break;
        default:
            throw new RuntimeException("unknown status!");
        }
    }

/**
     * OK数据包处理
     */
    private void handleOkPacket(byte[] data) {
        ResponseHandler respHand = responseHandler;
        if (respHand != null) {
            respHand.okResponse(data, source);
        }
    }

handleOkPacket 里面又做了一次选择,做为单个数据结点反回还是比较简单的,我们来看一下多数据结点的处理逻辑。
MyCat 学习笔记 第二十一篇 . mycat 源代码分析 中_第2张图片

io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler

@Override
    public void rowResponse(final byte[] row, final BackendConnection conn) {
        if (errorRepsponsed.get()) {
            // the connection has been closed or set to "txInterrupt" properly
            //in tryErrorFinished() method! If we close it here, it can
            // lead to tx error such as blocking rollback tx for ever.
            // @author Uncle-pan
            // @since 2016-03-25
            //conn.close(error);
            return;
        }
        lock.lock();
        try {
            RouteResultsetNode rNode = (RouteResultsetNode) conn.getAttachment();
            String dataNode = rNode.getName();
            if (dataMergeSvr != null) {
                // even through discarding the all rest data, we can't
                //close the connection for tx control such as rollback or commit.
                // So the "isClosedByDiscard" variable is unnecessary.
                // @author Uncle-pan
                // @since 2016-03-25
                dataMergeSvr.onNewRecord(dataNode, row);
            } else {
                // cache primaryKey-> dataNode
                if (primaryKeyIndex != -1) {
                    RowDataPacket rowDataPkg = new RowDataPacket(fieldCount);
                    rowDataPkg.read(row);
                    String primaryKey = new String(
                            rowDataPkg.fieldValues.get(primaryKeyIndex));
                    LayerCachePool pool = MycatServer.getInstance()
                            .getRouterservice().getTableId2DataNodeCache();
                    pool.putIfAbsent(priamaryKeyTable, primaryKey, dataNode);
                }
                row[3] = ++packetId;
                session.getSource().write(row);
            }

        } catch (Exception e) {
            handleDataProcessException(e);
        } finally {
            lock.unlock();
        }
    }

上面的代码块中的dataMergeSvr 即为多数据结点时最重要的数据合并处理类,我们再来看下mycat 到底是怎么来做数据合并的。

/**
     * process new record (mysql binary data),if data can output to client
     * ,return true
     * 
     * @param dataNode
     *            DN's name (data from this dataNode)
     * @param rowData
     *            raw data
     * @param conn
     */
    public boolean onNewRecord(String dataNode, byte[] rowData) {
        // 对于需要排序的数据,由于mysql传递过来的数据是有序的,
        // 如果某个节点的当前数据已经不会进入,后续的数据也不会入堆
        if (canDiscard.size() == rrs.getNodes().length) {
            // "END_FLAG" only should be added by MultiNodeHandler.rowEofResponse()
            // @author Uncle-pan
            // @since 2016-03-23
            //LOGGER.info("now we output to client");
            //addPack(END_FLAG_PACK);
            return true;
        }
        if (canDiscard.get(dataNode) != null) {
            return true;
        }
        final PackWraper data = new PackWraper();
        data.node = dataNode;
        data.data = rowData;
        addPack(data);
        return false;
    }

    /**
     * Add a row pack, and may be wake up a business thread to work if not running.
     * @param pack row pack
     * @return true wake up a business thread, otherwise false
     * 
     * @author Uncle-pan
     * @since 2016-03-23
     */
    private final boolean addPack(final PackWraper pack){
        packs.add(pack);
        if(running.get()){
            return false;
        }
        final MycatServer server = MycatServer.getInstance();
        server.getBusinessExecutor().execute(this);
        return true;
    }

这里就能看到这个DataMergeServer 还是另一个多线程处理机制的实现。
在run方法里寻找出最后一个数据包,并通过 outputMergeResult 写入前端连接的 write buffer queue。

// loop-on-packs
            for (; ; ) {
                final PackWraper pack = packs.poll();
                // async: handling row pack queue, this business thread should exit when no pack
                // @author Uncle-pan
                // @since 2016-03-23
                if(pack == null){
                    nulpack = true;
                    break;
                }
                // eof: handling eof pack and exit
                if (pack == END_FLAG_PACK) {
                    final int warningCount = 0;
                    final EOFPacket eofp   = new EOFPacket();
                    final ByteBuffer eof   = ByteBuffer.allocate(9);
                    BufferUtil.writeUB3(eof, eofp.calcPacketSize());
                    eof.put(eofp.packetId);
                    eof.put(eofp.fieldCount);
                    BufferUtil.writeUB2(eof, warningCount);
                    BufferUtil.writeUB2(eof, eofp.status);
                    final ServerConnection source = multiQueryHandler.getSession().getSource();
                    final byte[] array = eof.array();
                    multiQueryHandler.outputMergeResult(source, array, getResults(array));
                    break;
                }
                // merge: sort-or-group, or simple add
                final RowDataPacket row = new RowDataPacket(fieldCount);
                row.read(pack.data);
                if (grouper != null) {
                    grouper.addRow(row);
                } else if (sorter != null) {
                    if (!sorter.addRow(row)) {
                        canDiscard.put(pack.node, true);
                    }
                } else {
                    result.add(row);
                }
            }// rof

在io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler中调用最大的connection写入方法,再通过异步写出socket channel。

public void outputMergeResult(final ServerConnection source,
            final byte[] eof, List results) {
        try {
            lock.lock();
            ByteBuffer buffer = session.getSource().allocate();
            final RouteResultset rrs = this.dataMergeSvr.getRrs();

            // 处理limit语句
            int start = rrs.getLimitStart();
            int end = start + rrs.getLimitSize();

                        if (start < 0)
                start = 0;

            if (rrs.getLimitSize() < 0)
                end = results.size();

            if (end > results.size())
                end = results.size();

            for (int i = start; i < end; i++) {
                RowDataPacket row = results.get(i);
                if( prepared ) {
                    BinaryRowDataPacket binRowDataPk = new BinaryRowDataPacket();
                    binRowDataPk.read(fieldPackets, row);
                    binRowDataPk.packetId = ++packetId;
                    binRowDataPk.write(source);
                } else {
                    row.packetId = ++packetId;
                    buffer = row.write(buffer, source, true);
                }
            }

            eof[3] = ++packetId;
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("last packet id:" + packetId);
            }
            source.write(source.writeToBuffer(eof, buffer));

        } catch (Exception e) {
            handleDataProcessException(e);
        } finally {
            lock.unlock();
            dataMergeSvr.clear();
        }
    }

io.mycat.net.AbstractConnection

@Override
    public final void write(ByteBuffer buffer) {

        if (isSupportCompress()) {
            ByteBuffer newBuffer = CompressUtil.compressMysqlPacket(buffer, this, compressUnfinishedDataQueue);
            writeQueue.offer(newBuffer);
        } else {
            writeQueue.offer(buffer);
        }

        // if ansyn write finishe event got lock before me ,then writing
        // flag is set false but not start a write request
        // so we check again
        try {
            this.socketWR.doNextWriteCheck();
        } catch (Exception e) {
            LOGGER.warn("write err:", e);
            this.close("write err:" + e);
        }
    }

到这里为止,mycat 从后端多个数据库中拿到数据后,组合合并在一个响应里反馈客户端的流程大体上就这样子,再来补一张图看得会清楚一些。

MyCat 学习笔记 第二十一篇 . mycat 源代码分析 中_第3张图片

到这里为止,非常粗力度的过一下 mycat 的基础运行原理。虽然mycat 在一些极端情况下不稳定,虽然一些代码细节还有待优化,但这些都不影响 mycat 是目前见过最好的来自中国民间自发力量的开源项目,而且还有非常大的实际使用价值,真心赞。

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