Add ModelColumn#shouldIndex method (#8853)

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/annotation/Column.java

@@ -49,15 +49,13 @@ public @interface Column {
     int defaultValue() default 0;
 
     /**
-     * The column is just saved, never used in query.
+     * The column is just saved, never used as a query condition.
      */
     boolean storageOnly() default false;
 
     /**
-     * The column(field) is just indexed, never stored. Note: this feature only supported by elasticsearch and don't
-     * support mappings update due to ElasticSearch server's limitation.
-     *
-     * NOTICE, metrics should not use this, as the OAP core merges indices of metrics automatically.
+     * The column(field) is just indexed, never stored(not available in query projection).
+     * Note: this feature only supported by elasticsearch.
      */
     boolean indexOnly() default false;
 
@@ -66,7 +64,7 @@ public @interface Column {
      * storage implementation.
      *
      * Notice, different lengths may cause different types. Such as, over 16383 would make the type in MySQL to be
-     * MEDIUMTEXT, due to database varchar max=16383
+     * MEDIUMTEXT, due to database varchar max=16383.
      * @since 7.1.0
      */
     int length() default 200;

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/model/ModelColumn.java

@@ -99,4 +99,11 @@ public class ModelColumn {
         this.indexOnly = indexOnly;
         this.banyanDBExtension = banyanDBExtension;
     }
+
+    /**
+     * @return true means this column should be indexed, as it would be a query condition.
+     */
+    public boolean shouldIndex() {
+        return !storageOnly;
+    }
 }

oap-server/server-storage-plugin/storage-jdbc-hikaricp-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/jdbc/mysql/MySQLTableInstaller.java

@@ -76,7 +76,7 @@ public class MySQLTableInstaller extends H2TableInstaller {
                                       Model model) throws JDBCClientException {
         int indexSeq = 0;
         for (final ModelColumn modelColumn : model.getColumns()) {
-            if (!modelColumn.isStorageOnly() && modelColumn.getLength() < 256) {
+            if (modelColumn.shouldIndex() && modelColumn.getLength() < 256) {
                 final Class<?> type = modelColumn.getType();
                 if (List.class.isAssignableFrom(type)) {
                     for (int i = 0; i < maxSizeOfArrayColumn; i++) {