The mainstream distributed transaction processing scheme
In recent years, , With the widespread use of microservices , The business demands higher and higher distributed transaction processing capability of the system .
The early ones were based on XA Phase II of the protocol submission , Put the processing of distributed transactions in the database driver layer , It realizes no invasion to the business , But the locking time of data is very long , Low performance .
Now the mainstream TCC Transaction scheme and SAGA Business plan , Are based on the business compensation mechanism , Although there is no global lock , A high performance , But to some extent, it invades the business logic , It increases the development time and system maintenance cost of business developers .
burgeoning AT Transaction solutions , for example Seata and Seata-golang, Through the resource manager of the data source proxy layer RM Record SQL Rollback log , Submit with local transaction , Greatly reduce the data locking time , Good performance with little intrusion into the business . The disadvantage is that the supported language is relatively single , for example Seata Only support Java Language type microservices ,Seata-golang Only support Go Language type microservices .
In order to break through AT Transaction restrictions on business programming languages , Now the industry is going to DB Mesh Direction of development , By deploying transaction middleware in SideCar The way , Achieve the effect that any programming language can use distributed transaction middleware .
DBPack Is a database agent that handles distributed transactions , It can intercept MySQL Traffic , Generate the corresponding transaction rollback image , Through and with ETCD Coordinate the completion of distributed transactions , A high performance , And there is no invasion of business , It can automatically compensate SQL operation , Support access to any programming language .DBPack And support TCC Transaction mode , It can automatically compensate HTTP request . At present demo There has been a Java、Go、Python and PHP,TCC Of sample It's already on the way ,demo Examples can focus on dbpack-samples.
The latest version DBPack Not only support preprocessing sql sentence , And support text Type of sql.DBPack The latest version is also compatible php8 Of pdo_mysql Expand .Mysql The client is sending sql When executing the results , If there is no exception in the execution , The first packet sent is OKPacket, There is a flag bit in the package to identify sql Whether the request is in a transaction . As shown in the figure below
The contents of this package are ：
07 00 00 // front 3 Byte representation payload The length of is 7 Bytes
01 // sequence Sequence number of response , front 4 Bytes together make up OKPacket Of header
00 // identification payload by OKPacket
00 // affected row
00 // last insert id
03 00 // Status flags
00 00 // warning Number
dbpack Previous versions set the flag bit to 0,java、golang、.net core、php 8.0 Previous mysql driver Can coordinate affairs correctly ,php 8.0 Of pdo driver The flag bit will be verified , therefore php 8.0 The above version is in use dbpack When coordinating distributed transactions , Will throw out transaction not active abnormal . The latest version has fixed this problem .
The figure below is specific DBPack Transaction flow chart .
The transaction flow is briefly described as follows ：
- The client provides services to the aggregation layer DBPack Agent initiated HTTP request .
- DBPack Generate globally unique XID, Store in ETCD in . Note that the requested address and port point to DBPack, It does not directly point to reality API.
- If the global transaction is started successfully （ If it fails, the transaction will be ended directly ）, Aggregation layer services can be provided through HTTP header（X-Dbpack-Xid） Get XID 了 . here , Aggregate service invokes service 1 And transmission XID.
- service 1 Get XID, adopt DBPack agent , Register branch transactions （ Generate BranchID Etc , And store it to ETCD）.
- service 1 After the branch transaction of is registered successfully , Generate rollback image of local transaction , With local transactions commit.
- service 2 Conduct and service 1 The same procedure 4 and 5.
- Aggregation layer services are based on services 1 And the service 2 Result , Decide whether the global transaction is committed or rolled back , If it's a success , Then return to HTTP 200 to DBPack（ except 200 Other status codes will be DBPack Consider it a failure ）.DBPack to update ETCD The global transaction status in is global commit or rollback .
- service 1 And the service 2 Of DBPack, adopt ETCD Of watch Mechanism , Know whether the local branch transaction should be committed or rolled back （ If it is submitted , Delete the rollback log ; If it is rollback , Then rollback to the pre transaction image by rolling back the log ）.
- After all branch transactions are committed or rolled back , Aggregation layer services DBPack The coroutine of will detect that the transaction has been completed , Will be taken from ETCD Delete XID and BranchID And other transaction information .
This article will be PHP Language as an example , Describe in detail how to use PHP docking DBPack Complete distributed transactions . When actually using other languages , The docking process is similar .
Use PHP docking DBPack Implementing distributed transactions
precondition
- The business database is mysql database
- The business data sheet is innodb type
- The business data table must have a primary key
Step0: install ETCD
ETCD_VER=v3.5.3
# choose either URL
GOOGLE_URL=https://storage.googleapis.com/etcd
GITHUB_URL=https://github.com/etcd-io/etcd/releases/download
DOWNLOAD_URL=${GOOGLE_URL}
rm -f /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz
rm -rf /tmp/etcd-download-test && mkdir -p /tmp/etcd-download-test
curl -L ${DOWNLOAD_URL}/${ETCD_VER}/etcd-${ETCD_VER}-linux-amd64.tar.gz -o /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz
tar xzvf /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz -C /tmp/etcd-download-test --strip-components=1
rm -f /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz
/tmp/etcd-download-test/etcd --version
/tmp/etcd-download-test/etcdctl version
/tmp/etcd-download-test/etcdutl version
Step1: Create in the business database undo_log surface
undo_log Table is used to store rollback images of local transactions .
-- ----------------------------
-- Table structure for undo_log
-- ----------------------------
DROP TABLE IF EXISTS `undo_log`;
CREATE TABLE `undo_log` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`branch_id` bigint(20) NOT NULL,
`xid` varchar(100) NOT NULL,
`context` varchar(128) NOT NULL,
`rollback_info` longblob NOT NULL,
`log_status` int(11) NOT NULL,
`log_created` datetime NOT NULL,
`log_modified` datetime NOT NULL,
`ext` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `idx_unionkey` (`xid`,`branch_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Step2: Writing configuration files , docking DBPack
- aggregation-service It refers to the aggregation layer of microservices , Call all business interfaces .business-service It refers to the specific business interface .
- complete aggregation-service Configuration can refer to sample Inside config-aggregation To configure .
- complete business-service Configuration can refer to sample Inside config-order To configure
# to update distributed_transaction.etcd_config.endpoints
# to update listeners Configuration item , Adjust the address and port of the actual aggregation layer service
# to update filters Configuration item , Configure the aggregation layer service API endpoint
vim /path/to/your/aggregation-service/config-aggregation.yaml
# to update distributed_transaction.etcd_config.endpoints
# to update listeners Configuration item , Configure business database information , Include dbpack Port of agent
# to update data_source_cluster.dsn
vim /path/to/your/business-service/config-service.yaml
Step3: function DBPack
git clone [email protected]:cectc/dbpack.git
cd dbpack
# build on local env
make build-local
# build on production env
make build
./dist/dbpack start --config /path/to/your/config-aggregation.yaml
./dist/dbpack start --config /path/to/your/config-service.yaml
Step4: To configure vhost, monitor php Project port
With Nginx For example , The configuration is as follows
server {
listen 3001; # Exposed service port
index index.php index.html;
root /var/www/code/; # Business code root directory
location / {
try_files $uri /index.php?$args;
}
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass order-svc-app:9000; # php-fpm port
fastcgi_index index.php;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param PATH_INFO $fastcgi_path_info;
}
}
Step5: Write applications
aggregation service example
<?php
class AggregationSvc
{
public function CreateSo(string $xid, bool $rollback): bool
{
$createSoSuccess = $this->createSoRequest($xid);
if (!$createSoSuccess) {
return false;
}
$allocateInventorySuccess = $this->allocateInventoryRequest($xid);
if (!$allocateInventorySuccess) {
return false;
}
if ($rollback) {
return false;
}
return true;
}
// private function createSoRequest(string $xid) ...
// private function allocateInventoryRequest(string $xid) ...
}
$reqPath = strtok($_SERVER["REQUEST_URI"], '?');
$reaHeaders = getallheaders();
$xid = $reaHeaders['X-Dbpack-Xid'] ?? '';
if (empty($xid)) {
die('xid is not provided!');
}
$aggregationSvc = new AggregationSvc();
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
switch ($reqPath) {
case '/v1/order/create':
if ($aggregationSvc->CreateOrder($xid, false)) {
responseOK();
} else {
responseError();
}
case '/v1/order/create2':
if ($aggregationSvc->CreateSo($xid, true)) {
responseOK();
} else {
responseError();
}
break;
default:
die('api not found');
}
}
function responseOK() {
http_response_code(200);
echo json_encode([
'success' => true,
'message' => 'success',
]);
}
function responseError() {
http_response_code(400);
echo json_encode([
'success' => false,
'message' => 'fail',
]);
}
order service example
<?php
class OrderDB
{
private PDO $_connection;
private static OrderDB $_instance;
private string $_host = 'dbpack-order';
private int $_port = 13308;
private string $_username = 'dksl';
private string $_password = '123456';
private string $_database = 'order';
const insertSoMaster = "INSERT /*+ XID('%s') */ INTO order.so_master (sysno, so_id, buyer_user_sysno, seller_company_code,
receive_division_sysno, receive_address, receive_zip, receive_contact, receive_contact_phone, stock_sysno,
payment_type, so_amt, status, order_date, appid, memo) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,now(),?,?)";
const insertSoItem = "INSERT /*+ XID('%s') */ INTO order.so_item(sysno, so_sysno, product_sysno, product_name, cost_price,
original_price, deal_price, quantity) VALUES (?,?,?,?,?,?,?,?)";
public static function getInstance(): OrderDB
{
if (empty(self::$_instance)) {
self::$_instance = new self();
}
return self::$_instance;
}
private function __construct()
{
try {
$this->_connection = new PDO(
"mysql:host=$this->_host;port=$this->_port;dbname=$this->_database;charset=utf8",
$this->_username,
$this->_password,
[
PDO::ATTR_PERSISTENT => true,
PDO::ATTR_EMULATE_PREPARES => false, // to let DBPack handle prepread sql
]
);
} catch (PDOException $e) {
die($e->getMessage());
}
}
private function __clone()
{
}
public function getConnection(): PDO
{
return $this->_connection;
}
public function createSo(string $xid, array $soMasters): bool
{
$this->getConnection()->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
try {
$this->getConnection()->beginTransaction();
foreach ($soMasters as $master) {
if (!$this->insertSo($xid, $master)) {
throw new PDOException("failed to insert soMaster");
}
}
$this->getConnection()->commit();
} catch (PDOException $e) {
$this->getConnection()->rollBack();
return false;
}
return true;
}
private function insertSo(string $xid, array $soMaster): bool
{
// insert into so_master, so_item ...
}
}
$reqPath = strtok($_SERVER["REQUEST_URI"], '?');
$reqHeaders = getallheaders();
$xid = $reqHeaders['Xid'] ?? '';
if (empty($xid)) {
die('xid is not provided!');
}
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
if ($reqPath === '/createSo') {
$reqBody = file_get_contents('php://input');
$soMasters = json_decode($reqBody, true);
$orderDB = OrderDB::getInstance();
$result = $orderDB->createSo($xid, $soMasters);
if ($result) {
responseOK();
} else {
responseError();
}
}
}
function responseOK() {
http_response_code(200);
echo json_encode([
'success' => true,
'message' => 'success',
]);
}
function responseError() {
http_response_code(400);
echo json_encode([
'success' => false,
'message' => 'fail',
]);
}
Step6: Access the aggregation layer business interface
curl -X{HTTP Method} http://localhost:{DBPack Listening aggregation layer service port }/{ Aggregation layer services API endpoint}
Points of attention
- Whether to use mysqli drive 、pdo_mysql drive , Or through
mysql_connect()Connect to database (<=php5.4), staystart transaction;After the start , Subsequent business operations must be carried out on the same database connection . - DBPack adopt xid（ Global transactions are unique ID） Propagate... In the context of a transaction , The business executed by the business database SQL In the sentence , Need to add xid notes , such DBPack According to xid Deal with the corresponding transaction . for example
insert /*+ XID('%s') */ into xx ...;
Reference link
- dbpack: https://github.com/CECTC/dbpack
- dbpack-samples: https://github.com/CECTC/dbpack-samples
- dbpack-doc: https://github.com/CECTC/dbpack-doc
- Seata-gplang: https://github.com/opentrx/seata-golang
- Seata: https://github.com/seata/seata
- AT Transaction model design ：https://seata.io/zh-cn/blog/seata-at-mode-design.html
Author's brief introduction
Buhehe . Worked in Rakuten, Japan Rakuten CNTD, ren Application Engineer, be familiar with AT Business 、Seata-golang and DBPack.GitHub：https://github.com/bohehe
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