聊聊claudb的transaction command

序

本文主要研究一下claudb的transaction command

TransactionState

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/TransactionState.java

public class TransactionState implements Iterable<Request> { private List<Request> requests = new LinkedList<>();​ public void enqueue(Request request) {   requests.add(request); }​ public int size() {   return requests.size(); }​ @Override public Iterator<Request> iterator() {   return requests.iterator(); }}

• TransactionState實現了Iterable<Request>接口，它定義了requests屬性，提供了enqueue方法將request添加到requests中

MultiCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/MultiCommand.java

@Command(&34;)@TxIgnorepublic class MultiCommand implements DBCommand {​ private static final String TRASACTION_KEY = &34;;​ @Override public RedisToken execute(Database db, Request request) {   if (!isTxActive(request.getSession())) {     createTransaction(request.getSession());     return responseOk();   } else {     return error(&34;);   } }​ private void createTransaction(Session session) {   session.putValue(TRASACTION_KEY, new TransactionState()); }​ private boolean isTxActive(Session session) {   return session.getValue(TRASACTION_KEY).isPresent(); }}

• MultiCommand實現了DBCommand接口，其execute方法先判斷isTxActive，非active的話才createTransaction

ExecCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/ExecCommand.java

@Command(&34;)@TxIgnorepublic class ExecCommand implements DBCommand {​ @Override public RedisToken execute(Database db, Request request) {   Option<TransactionState> transaction = getTransactionIfExists(request.getSession());   if (transaction.isPresent()) {     DBServerContext server = getClauDB(request.getServerContext());     List<RedisToken> responses = new ArrayList<>();     for (Request queuedRequest : transaction.get()) {       responses.add(executeCommand(server, queuedRequest));     }     return RedisToken.array(responses);   } else {     return RedisToken.error(&34;);   } }​ private RedisToken executeCommand(DBServerContext server, Request queuedRequest) {   RespCommand command = server.getCommand(queuedRequest.getCommand());   return command.execute(queuedRequest); }​ private Option<TransactionState> getTransactionIfExists(Session session) {   return session.removeValue(&34;); }}

• ExecCommand實現了DBCommand接口，其execute方法先通過getTransactionIfExists獲取transaction，若transaction不存在則報錯，存在的話則遍歷transaction的queuedRequest，挨個執行executeCommand(server, queuedRequest)

DiscardCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/DiscardCommand.java

@Command(&34;)@TxIgnorepublic class DiscardCommand implements DBCommand {​ private static final String TX_KEY = &34;;​ @Override public RedisToken execute(Database db, Request request) {   removeTransactionIfExists(request.getSession());​   return RedisToken.responseOk(); }​ private Option<TransactionState> removeTransactionIfExists(Session session) {   return session.removeValue(TX_KEY); }}

• DiscardCommand實現了DBCommand接口，其execute方法執行removeTransactionIfExists(request.getSession())

小結

claudb transaction相關的command有MultiCommand、ExecCommand、DiscardCommand

doc

• transaction