[jira] [Created] (IMPALA-8366) Consistent synchronization model for Db updates

["Vihang Karajgaonkar (JIRA)" <ji...@apache.org>]

Vihang Karajgaonkar created IMPALA-8366:
-------------------------------------------

             Summary: Consistent synchronization model for Db updates
                 Key: IMPALA-8366
                 URL: https://issues.apache.org/jira/browse/IMPALA-8366
             Project: IMPALA
          Issue Type: Improvement
          Components: Catalog
            Reporter: Vihang Karajgaonkar


The synchronization model of updates to {{Db}} is different than for {{Table}}. For example, adding a new function to a Db take a lock on {{functions_}} in a synchronized block below:

{code}
public boolean addFunction(Function fn, boolean addToDbParams) {
    Preconditions.checkState(fn.dbName().equals(getName()));
    synchronized (functions_) {
      if (getFunction(fn, Function.CompareMode.IS_INDISTINGUISHABLE) != null) {
        return false;
      }
      List<Function> fns = functions_.get(fn.functionName());
      if (fns == null) {
        fns = new ArrayList<>();
        functions_.put(fn.functionName(), fns);
      }
      if (addToDbParams && !addFunctionToDbParams(fn)) return false;
      fns.add(fn);
      Collections.sort(fns, FunctionUtils.FUNCTION_RESOLUTION_ORDER);
      return true;
    }
  }
{code}

While this works for most cases, it is confusing. Any updates to {{Table}} ideally should take a lock on {{mestoreDdlLock_}}, {{catalogVersion_}} and the table lock itself in that order.

While in case of Db updates, changes are done in-place without taking a write lock on {{catalogVersion_}}. This can cause problems like the one described in IMPALA-8312 where readers can see race conditions during updates to the Db object. It would be good and consistent if we take readlock on {{catalogVersion_}} too so that it is less confusing and cleaner.



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