GeezerVison

This adds a provider for VoltDB, an in-memory, partitioned, ACID SQL database. We have run it against VoltDB for several weeks, single nodes and clusters, and it has found more than seventy bugs, most of them wrong results.

What it adds

• The provider (src/sqlancer/voltdb): schema, data and typed expression generators over VoltDB's SQL. It covers replicated and partitioned tables, indexes, materialized views, stored procedures and streams, and its connection goes through the VoltDB JDBC driver (org.voltdb:voltdbclient).
• The common oracles: NoREC, TLP (WHERE, DISTINCT, HAVING, aggregates) and PQS. The provider evaluates VoltDB's expressions itself for PQS.
• Oracles for VoltDB's own features:
  • parameterized statements, materialized views, LIMIT/OFFSET, subqueries, window functions, set operations, derived tables and CTEs;
  • stored procedures, schema changes and the plan cache, geospatial functions;
  • differential query plans (PLANS) and streams.
• Oracles that need a cluster set up for them, each behind an option: permissions with security on, durability across a whole-cluster crash, XDCR convergence, and a mirror cluster running another version (DIFF).
• src/sqlancer/voltdb/README.md describes each oracle and option.

Changes to shared code

They are in the first commit, kept apart from the provider:

• GlobalState and SQLQueryAdapter.checkException pass an IgnoreMeException through instead of wrapping it in an AssertionError. A provider's connection can then skip a statement or a database. VoltDB's does this after a node failure, when a statement may or may not have committed.
• CompositeTestOracle records the oracle that ran last before running it. getLastQueryString then names the oracle that failed, and its reproducer is returned, so --use-reducer works with more than one oracle.
• SQLancerResultSet.getObject(int).

Testing

• mvn verify passes, including checkstyle, PMD, SpotBugs and check_names.py (the provider has its entry).
• TestVoltDB runs the main oracles against a server on localhost:21212 when VOLTDB_AVAILABLE=true, as the other servers' tests do.

Not in this PR

• CI. VoltDB's public image, voltactivedata/volt-developer-edition, needs a license key, which a workflow would have to hold as a secret. We will follow up with a CI job once we have a key we can give the project, as CONTRIBUTING.md allows.
• Ticket numbers. Code comments name issues in VoltDB's tracker, such as ENG-30583, which are not public. --avoid-known-bugs true (the default) steers the generators around those bugs. Each workaround's comment says what it avoids, so it can be removed once the bug is fixed.

We would be glad to adjust anything to fit the project's conventions.