diff --git a/src/rproc/InfileMerger.cc b/src/rproc/InfileMerger.cc
index 487355722..f928ec3f6 100644
--- a/src/rproc/InfileMerger.cc
+++ b/src/rproc/InfileMerger.cc
@@ -102,6 +102,11 @@ std::string getTimeStampId() {
 
 const char JOB_ID_BASE_NAME[] = "jobId";
 size_t const MB_SIZE_BYTES = 1024 * 1024;
+
+/// @return Error info on the last operation with MySQL
+string lastMysqlError(MYSQL* mysql) {
+    return "error: " + string(mysql_error(mysql)) + ", errno: " + to_string(mysql_errno(mysql));
+}
 }  // anonymous namespace
 
 namespace lsst::qserv::rproc {
@@ -349,27 +354,34 @@ bool InfileMerger::_applyMysqlMyIsam(std::string const& query) {
                 sleep(1);
                 lock.lock();
             } else {
-                LOGS(_log, LOG_LVL_ERROR, "InfileMerger::_applyMysql _setupConnection() failed!!!");
+                LOGS(_log, LOG_LVL_ERROR,
+                     "InfileMerger::_applyMysqlMyIsam _setupConnectionMyIsam() failed!!!");
                 return false;  // Reconnection failed. This is an error.
             }
         }
     }
 
     int rc = mysql_real_query(_mysqlConn.getMySql(), query.data(), query.size());
-    return rc == 0;
+    if (rc == 0) return true;
+    LOGS(_log, LOG_LVL_ERROR,
+         "InfileMerger::_applyMysqlMyIsam mysql_real_query() " + ::lastMysqlError(_mysqlConn.getMySql()));
+    return false;
 }
 
 bool InfileMerger::_applyMysqlInnoDb(std::string const& query) {
     mysql::MySqlConnection mySConn(_config.mySqlConfig);
     if (!mySConn.connected()) {
         if (!_setupConnectionInnoDb(mySConn)) {
-            LOGS(_log, LOG_LVL_ERROR, "InfileMerger::_applyMysql _setupConnection() failed!!!");
+            LOGS(_log, LOG_LVL_ERROR, "InfileMerger::_applyMysqlInnoDb _setupConnectionInnoDb() failed!!!");
             return false;  // Reconnection failed. This is an error.
         }
     }
 
     int rc = mysql_real_query(mySConn.getMySql(), query.data(), query.size());
-    return rc == 0;
+    if (rc == 0) return true;
+    LOGS(_log, LOG_LVL_ERROR,
+         "InfileMerger::_applyMysqlInnoDb mysql_real_query() " + ::lastMysqlError(mySConn.getMySql()));
+    return false;
 }
 
 bool InfileMerger::_setupConnectionInnoDb(mysql::MySqlConnection& mySConn) {