MXS-1621: Skip unneeded ALTER TABLE operations

Some ALTER TABLE operations (e.g. ADD INDEX) are not useful to the
avrorouter. These need to be detected and skipped.

server/modules/routing/avrorouter/avro_file.c

@@ -1021,6 +1021,40 @@ void unify_whitespace(char *sql, int len)
     }
 }
 
+/**
+ * A very simple function for stripping auto-generated executable comments
+ *
+ * Note that the string will not strip the trailing part of the comment, making
+ * the SQL invalid.
+ *
+ * @param sql String to modify
+ * @param len Pointer to current length of string, updated to new length if
+ *            @c sql is modified
+ */
+static void strip_executable_comments(char *sql, int* len)
+{
+    if (strncmp(sql, "/*!", 3) == 0 || strncmp(sql, "/*M!", 4) == 0)
+    {
+        // Executable comment, remove it
+        char* p = sql + 3;
+        if (*p == '!')
+        {
+            p++;
+        }
+
+        // Skip the versioning part
+        while (*p && isdigit(*p))
+        {
+            p++;
+        }
+
+        int n_extra = p - sql;
+        int new_len = *len - n_extra;
+        memmove(sql, sql + n_extra, new_len);
+        *len = new_len;
+    }
+}
+
 /**
  * @brief Handling of query events
  *
@@ -1046,6 +1080,7 @@ void handle_query_event(AVRO_INSTANCE *router, REP_HEADER *hdr, int *pending_tra
     sql = tmp;
     len = tmpsz;
     unify_whitespace(sql, len);
+    strip_executable_comments(sql, &len);
     sql[len] = '\0';
 
     static bool warn_not_row_format = true;
@@ -1107,7 +1142,7 @@ void handle_query_event(AVRO_INSTANCE *router, REP_HEADER *hdr, int *pending_tra
         }
         else
         {
-            MXS_ERROR("Alter statement to a table with no create statement.");
+            MXS_ERROR("Alter statement to table '%s' has no preceding create statement.", ident);
         }
     }
     /* A transaction starts with this event */

server/modules/routing/avrorouter/avro_rbr.c

@@ -337,9 +337,9 @@ bool handle_row_event(AVRO_INSTANCE *router, REP_HEADER *hdr, uint8_t *ptr)
         }
         else if (ncolumns == map->columns && create->columns != map->columns)
         {
-            MXS_ERROR("Table map event has a different column "
+            MXS_ERROR("Table map event has a different column count for table "
-                      "count for table %s.%s than the CREATE TABLE statement.",
+                      "%s.%s than the CREATE TABLE statement. Possible "
-                      map->database, map->table);
+                      "unsupported DDL detected.", map->database, map->table);
         }
         else
         {

server/modules/routing/avrorouter/avro_schema.c

@@ -1392,6 +1392,14 @@ int get_column_index(TABLE_CREATE *create, const char *tok, int len)
     char safe_tok[len + 2];
     memcpy(safe_tok, tok, len);
     safe_tok[len] = '\0';
+
+    if (*safe_tok == '`')
+    {
+        int toklen = strlen(safe_tok) - 2; // Token length without backticks
+        memmove(safe_tok, safe_tok + 1, toklen); // Overwrite first backtick
+        safe_tok[toklen] = '\0'; // Null-terminate the string before the second backtick
+    }
+
     fix_reserved_word(safe_tok);
 
     for (int x = 0; x < create->columns; x++)
@@ -1406,6 +1414,35 @@ int get_column_index(TABLE_CREATE *create, const char *tok, int len)
     return idx;
 }
 
+static bool not_column_operation(const char* tok, int len)
+{
+    const char* keywords[] =
+    {
+        "PRIMARY",
+        "UNIQUE",
+        "FULLTEXT",
+        "SPATIAL",
+        "PERIOD",
+        "PRIMARY",
+        "KEY",
+        "KEYS",
+        "INDEX",
+        "FOREIGN",
+        "CONSTRAINT",
+        NULL
+    };
+
+    for (int i = 0; keywords[i]; i++)
+    {
+        if (tok_eq(tok, keywords[i], strlen(keywords[i])))
+        {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 bool table_create_alter(TABLE_CREATE *create, const char *sql, const char *end)
 {
     const char *tbl = strcasestr(sql, "table"), *def;
@@ -1431,7 +1468,12 @@ bool table_create_alter(TABLE_CREATE *create, const char *sql, const char *end)
 
             if (tok)
             {
-                if (tok_eq(tok, "column", len))
+                if (not_column_operation(tok, len))
+                {
+                    MXS_INFO("Statement doesn't affect columns, not processing: %s", sql);
+                    return true;
+                }
+                else if (tok_eq(tok, "column", len))
                 {
                     // Skip the optional COLUMN keyword
                     tok = get_tok(tok + len, &len, end);