Bug#20685859 ENABLE STAGES WITH PROGRESS BY DEFAULT FOR EASE OF USE

Before this fix, every "stage/%" instrument is disabled by default.

With this fix, stage instruments that provide online progress monitoring
are enabled and timed by default.

The list of stage instruments with online progress is currently:

- stage/sql/copy to tmp table
- stage/innodb/alter table (end)
- stage/innodb/alter table (flush)
- stage/innodb/alter table (insert)
- stage/innodb/alter table (log apply index)
- stage/innodb/alter table (log apply table)
- stage/innodb/alter table (merge sort)
- stage/innodb/alter table (read PK and internal sort)
- stage/innodb/buffer pool load

Author: marcalff

storage/perfschema/pfs_instr_class.cc

@@ -1388,8 +1388,20 @@ PFS_stage_key register_stage_class(const char *name,
     init_instr_class(entry, name, name_length, flags, PFS_CLASS_STAGE);
     entry->m_prefix_length= prefix_length;
     entry->m_event_name_index= index;
-    entry->m_enabled= false; /* disabled by default */
-    entry->m_timed= false;
+
+    if (flags & PSI_FLAG_STAGE_PROGRESS)
+    {
+      /* Stages with progress information are enabled and timed by default */
+      entry->m_enabled= true;
+      entry->m_timed= true;
+    }
+    else
+    {
+      /* Stages without progress information are disabled by default */
+      entry->m_enabled= false;
+      entry->m_timed= false;
+    }
+
     /* Set user-defined configuration options for this instrument */
     configure_instr_class(entry);
     PFS_atomic::add_u32(&stage_class_allocated_count, 1);