Message-ID: <gh-pgjdbc-pgjdbc-3781@github.com>
From: "ShenFeng312 (@ShenFeng312)" <noreply+ShenFeng312@github.com>
To: "pgjdbc/pgjdbc" <noreply+pgjdbc-pgjdbc@github.com>
Date: Fri, 22 Aug 2025 04:40:35 +0000
Subject: [pgjdbc/pgjdbc] issue #3781: Performance Optimization: PgPreparedStatement.getMetaData Should Not Use QUERY_ONESHOT
List-Id: <gh-pgjdbc-pgjdbc.github.com>
X-GitHub-Author-Id: 49786112
X-GitHub-Author-Login: ShenFeng312
X-GitHub-Issue: 3781
X-GitHub-Repo: pgjdbc/pgjdbc
X-GitHub-State: closed
X-GitHub-Type: issue
X-GitHub-Url: https://github.com/pgjdbc/pgjdbc/issues/3781
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Description:
Currently, `PgPreparedStatement.getMetaData` uses `QUERY_ONESHOT` before `execute` is invoked, which results in `query.setStatementName(statementName, deallocateEpoch)` not being executed. Consequently, the binary protocol cannot be used to receive the result set.

```java
    if (!oneShot) {
      // Generate a statement name to use.
      statementName = "S_" + (nextUniqueID++);

      // And prepare the new statement.
      // NB: Must clone the OID array, as it's a direct reference to
      // the SimpleParameterList's internal array that might be modified
      // under us.
      query.setStatementName(statementName, deallocateEpoch);
      query.setPrepareTypes(typeOIDs);
      registerParsedQuery(query, statementName);
    }
```

```java
public @Nullable ResultSetMetaData getMetaData() throws SQLException {
    checkClosed();
    ResultSet rs = getResultSet();

    if (rs == null || ((PgResultSet) rs).isResultSetClosed()) {
      // OK, we haven't executed it yet, or it was closed
      // we've got to go to the backend
      // for more info. We send the full query, but just don't
      // execute it.

      int flags = QueryExecutor.QUERY_ONESHOT | QueryExecutor.QUERY_DESCRIBE_ONLY
          | QueryExecutor.QUERY_SUPPRESS_BEGIN;
      StatementResultHandler handler = new StatementResultHandler();
      connection.getQueryExecutor().execute(preparedQuery.query, preparedParameters, handler, 0, 0,
          flags);
      ResultWrapper wrapper = handler.getResults();
      if (wrapper != null) {
        rs = wrapper.getResultSet();
      }
    }

    if (rs != null) {
      return rs.getMetaData();
    }

    return null;
  }
```