Detect cases where system_config has too many rows

Sometimes when setting up a new server a user can find a way to
insert multiple rows into the system_config table.  Instead of
honoring one of them seemingly at ranodm (and ignoring the other
rows that may have critical data in them) we now abort at startup
with a description of the problem.

Signed-off-by: Shawn O. Pearce <sop@google.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/main/java/com/google/gerrit/server/GerritServer.java b/src/main/java/com/google/gerrit/server/GerritServer.java
index 19729fc9ec..e4aa34b576 100644
--- a/src/main/java/com/google/gerrit/server/GerritServer.java
+++ b/src/main/java/com/google/gerrit/server/GerritServer.java
@@ -76,6 +76,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.concurrent.TimeUnit;
@@ -634,7 +635,17 @@ public class GerritServer {
       }
 
       if (sVer.versionNbr == ReviewDb.VERSION) {
-        sConfig = c.systemConfig().get(new SystemConfig.Key());
+        final List<SystemConfig> all = c.systemConfig().all().toList();
+        switch (all.size()) {
+          case 0:
+            throw new OrmException("system_config table is empty");
+          case 1:
+            sConfig = all.get(0);
+            break;
+          default:
+            throw new OrmException("system_config must have exactly 1 row;"
+                + " found " + all.size() + " rows instead");
+        }
 
       } else {
         throw new OrmException("Unsupported schema version " + sVer.versionNbr