Page Comparison

Current approach to working with transactions in RMB

To enable the work with a database in FOLIO project there is a custom solution implemented on top of the VERT.X Postgres Client. The main feature of working with RMB and VERT.X is the usage of the asynchronous approach. Sequential execution of operations requires handling the completion of each operation and occurring errors. Each subsequent operation can be executed only if the previous one is succeeded. In order to maintain data consistency there is a need to execute the operations in transaction and be able to rollback the changes in case an error occurred. At the moment, this possibility is implemented as follows:

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The First and the last operations RMB PostgresClient does automatically

Example method with two operation in scope of one transaction

public Future<Void> example() {
  Future future = Future.future();
  PostgresClient client = PostgresClient.getInstance(vertx, tenantId);
  // start tx
  client.startTx(tx -> {
    // first operation
    client.get(tx, "upload_definition", UploadDefinition.class, new Criterion(), true, false, getHandler -> {
      if (getHandler.succeeded()) {
        // second operation
        client.save(tx, "upload_definition", UUID.randomUUID().toString(), getHandler.result(), saveHandler -> {
          if (saveHandler.succeeded()) {
            client.endTx(tx, endHandler -> {
              if (endHandler.succeeded()) {
                future.succeeded();
              } else {
                client.rollbackTx(tx, rollbackHandler -> {
                  future.fail(getHandler.cause());
                });
              }
            });
          } else {
            client.rollbackTx(tx, rollbackHandler -> {
              future.fail(getHandler.cause());
            });
          }
        });
      } else {
        client.rollbackTx(tx, rollbackHandler -> {
          future.fail(getHandler.cause());
        });
      }
    });
  });
  return future;
}

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• The inability to simultaneously run multiple operations within a single connection

  Code Block
  language java linenumbers true
  public void test1() { PostgresClient client = PostgresClient.getInstance(vertx, "diku"); client.startTx(tx -> { for (int i = 0; i < 5; i++) { // ConnectionStillRunningQueryException: [2] - There is a query still being run here - race -> false client.save(tx, UPLOAD_DEFINITION_TABLE, UUID.randomUUID().toString(), new UploadDefinition().withId(UUID.randomUUID().toString()), reply -> { if (reply.succeeded()) { System.out.println(reply.result()); } else { System.out.println(reply.cause().getLocalizedMessage()); } }); } }); }

  
  

• A transaction is used within one connection and, accordingly, all subsequent actions must be performed in handlers and all errors must be manually processed. "Callback hell" as a result
• There is no support for some kind of persistence context and all locks must be done manually in the database by separate requests
• There is no possibility to easily manage the transaction isolation level at the application level
• Since all objects are stored in JSON format in the database, there is no way to be sure that the data is stored correctly. At the moment there is an opportunity to save any JSON in any table
• Because of the storage of objects in JSON format, it is not possible to build durable relationships between entities
• It is necessary either to store all the links in one big JSON object in one table or put them into the other tables and create primary keys that do not guarantee contact with another entity. Need to make several requests to load data by primary keys and insert them into the parent object
• RMB don't have all needed methods for working with transactions and queries.
• RMB don't have method for get() method that using custom SQL script with transaction support

Possible solutions

• Refactoring  Refactoring of the RMB's PostgresClient and add a couple of new methods for updating with blocking, transactions and loading records with the blocking of the record itself in the scope of the transaction

  • Create a single approach to query data from the database. For now get, save, update, delete methods at PostgresClient have different query mechanisms: CQLWrapper, Criterion, UUID. Need to create a wrapper for the querying functionality or encapsulate this logic and add a possibility to run custom SQL with “SELECT” statements.

  • Add methods for an update with row blocking in the table.

  • Add batchUpdate method

  • Change saveBatch method. For now, it doesn’t work with ids in the table

• Investigate the possibility of using other database tools. Conduct a study on the compatibility of the vert.x framework and existing solutions for the database, perhaps even synchronous solutions.

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