{ "date": "2016-12-19T19:42:50", "slug": "oracle-12cr2-awr-views-in-multitenant", "link": "https://www.dbi-services.com/blog/oracle-12cr2-awr-views-in-multitenant/", "title": { "rendered": "Oracle 12cR2: AWR views in multitenant" }, "content": { "rendered": "

By Franck Pachot

\n

.
\nIn a previous post I explained how the AWR views have changed between 12.1.0.1 and 12.1.0.2 and now in 12.2.0.1 they have changed again. This is a good illustration of multitenant object link usage.
\n
\nWhat’s new in 12cR2 is the ability to run AWR snapshots at CDB or PDB level. I really think that it makes more sense to read an AWR report at CDB level because it’s about analysing the system (=instance) activity. But with PDBaaS I can understand the need to give a report to analyse PDB sessions, resource and statements.

\n

I’ll start with the conclusion – a map of AWR view to show which ones read from CDB level snapshots, or PDB snapshots, or both:

\n

\"C0DLx2GXEAALIG4\"
\nI’ll explain AWR reports in a future post. Basically when you run awrrpt.sql from CDB$ROOT you get CDB snapshots and when you run it from PDB you have the choice.

\n

In the diagram above, just follow the arrows to know which view reads from PDB or CDB or both. You see two switches between the root and the PDB: data link for one way and common view for the other way. Note that all are metadata links so switches occurs also at parse time.

\n

WRM$_

\n

Let’s start from the table where AWR snapshots are stored:

\n
\nSQL> select owner,object_name,object_type,sharing from dba_objects where object_name='WRM$_SNAPSHOT';\n \nOWNER OBJECT_NAME                    OBJECT_TYPE             SHARING\n----- ------------------------------ ----------------------- ------------------\nSYS   WRM$_SNAPSHOT                  TABLE                   METADATA LINK\n
\n

This is a table. METADATA LINK means that the structure is the same in all containers, but data is different.

\n

I have the following containers:

\n
\nSQL> select con_id,dbid,name from v$containers;\n \n    CON_ID       DBID NAME\n---------- ---------- ------------------------------\n         1  904475458 CDB$ROOT\n         2 2066620152 PDB$SEED\n         3 2623271973 PDB1\n
\n

From CDB$ROOT I see data for the CDB:

\n
\nSQL> select dbid,count(*) from WRM$_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n
\n

and from PDB I see snapshots taken from PDB:

\n
\nSQL> alter session set container=PDB1;\nSession altered.\n \nSQL> select dbid,count(*) from WRM$_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n2623271973         79\n
\n

So remember, CDB$ROOT has 91 snapshots with DBID= 904475458 and PDB1 has 79 snapshots with DBID=2623271973

\n

AWR_ROOT_ and AWR_PDB_

\n

Views on WRM$_SNAPSHOT are referenced in DBA_DEPENDENCIES:

\n
\nSQL> select owner,name,type from dba_dependencies where referenced_name='WRM$_SNAPSHOT' and type like 'VIEW';\n \nOWNER NAME                           TYPE\n----- ------------------------------ -------------------\nSYS   AWR_ROOT_SNAPSHOT              VIEW\nSYS   AWR_ROOT_SYSSTAT               VIEW\nSYS   AWR_ROOT_ACTIVE_SESS_HISTORY   VIEW\nSYS   AWR_ROOT_ASH_SNAPSHOT          VIEW\nSYS   AWR_PDB_SNAPSHOT               VIEW\nSYS   AWR_PDB_ACTIVE_SESS_HISTORY    VIEW\nSYS   AWR_PDB_ASH_SNAPSHOT           VIEW\n
\n

I’m interested in views that show snapshot information: AWR_ROOT_SNAPSHOT and AWR_PDB_SNAPSHOT

\n
\nSQL> select owner,object_name,object_type,sharing from dba_objects where object_name in ('AWR_ROOT_SNAPSHOT','AWR_PDB_SNAPSHOT') order by 3;\n \nOWNER  OBJECT_NAME                    OBJECT_TYPE             SHARING\n------ ------------------------------ ----------------------- ------------------\nPUBLIC AWR_ROOT_SNAPSHOT              SYNONYM                 METADATA LINK\nPUBLIC AWR_PDB_SNAPSHOT               SYNONYM                 METADATA LINK\nSYS    AWR_ROOT_SNAPSHOT              VIEW                    DATA LINK\nSYS    AWR_PDB_SNAPSHOT               VIEW                    METADATA LINK\n
\n

Besides the synonyms, we have a metadata link view AWR_PDB_SNAPSHOT and a data link view AWR_ROOT_SNAPSHOT. The data link one means that it switches to CDB$ROOT when queried from a PDB. Here is the definition:

\n
\nSQL> select owner,view_name,container_data,text from dba_views where view_name in ('AWR_ROOT_SNAPSHOT','AWR_PDB_SNAPSHOT');\n \nOWNER  VIEW_NAME                      C TEXT\n------ ------------------------------ - --------------------------------------------------------------------------------\nSYS    AWR_ROOT_SNAPSHOT              Y select snap_id, dbid, instance_number, startup_time,\n                                               begin_interval_time, end_interval_time,\n                                               flush_elapsed, snap_level, error_count, snap_flag, snap_timezone,\n                                               decode(con_dbid_to_id(dbid), 1, 0, con_dbid_to_id(dbid)) con_id\n                                        from WRM$_SNAPSHOT\n                                        where status = 0\n \nSYS    AWR_PDB_SNAPSHOT               N select snap_id, dbid, instance_number, startup_time,\n                                               begin_interval_time, end_interval_time,\n                                               flush_elapsed, snap_level, error_count, snap_flag, snap_timezone,\n                                               decode(con_dbid_to_id(dbid), 1, 0, con_dbid_to_id(dbid)) con_id\n                                        from WRM$_SNAPSHOT\n                                        where status = 0\n
\n

Same definition. The difference is that AWR_PDB_SNAPSHOT reads from the current container but AWR_ROOT_SNAPSHOT being a DATA LINK always read from CDB$ROOT.

\n

This is what we can see:

\n
\nSQL> alter session set container=CDB$ROOT;\nSession altered.\n \nSQL> select dbid,count(*) from AWR_ROOT_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n \nSQL> select dbid,count(*) from AWR_PDB_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n \nSQL> alter session set container=PDB1;\nSession altered.\n \nSQL> select dbid,count(*) from AWR_ROOT_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n
\n

This query when run in PDB1 displays the 91 snapshots from the CDB.

\n
\nSQL> select dbid,count(*) from AWR_PDB_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n2623271973         79\n
\n

This one shows what is in the current container.

\n

Those are the views used by the AWR report, depending on the AWR location choice. But what about the DBA_HIST_ views that we know and use from previous versions?

\n

DBA_HIST_ and CDB_HIST_

\n

I continue to follow the dependencies:

\n
\nSQL> select owner,name,type from dba_dependencies where referenced_name in ('AWR_ROOT_SNAPSHOT','AWR_PDB_SNAPSHOT') and name like '%SNAPSHOT' order by 3;\n \nOWNER  NAME                           TYPE\n------ ------------------------------ -------------------\nPUBLIC AWR_ROOT_SNAPSHOT              SYNONYM\nPUBLIC AWR_PDB_SNAPSHOT               SYNONYM\nSYS    DBA_HIST_SNAPSHOT              VIEW\nSYS    CDB_HIST_SNAPSHOT              VIEW\n \nSQL> select owner,object_name,object_type,sharing from dba_objects where object_name in ('CDB_HIST_SNAPSHOT','DBA_HIST_SNAPSHOT');\n \nOWNER  OBJECT_NAME                    OBJECT_TYPE             SHARING\n------ ------------------------------ ----------------------- ------------------\nSYS    DBA_HIST_SNAPSHOT              VIEW                    METADATA LINK\nSYS    CDB_HIST_SNAPSHOT              VIEW                    METADATA LINK\nPUBLIC DBA_HIST_SNAPSHOT              SYNONYM                 METADATA LINK\nPUBLIC CDB_HIST_SNAPSHOT              SYNONYM                 METADATA LINK\n
\n

Here are the views I’m looking for. They are metadata link only. Not data link. This means that they do not switch to CDB$ROOT.

\n

But there’s more in the view definition:

\n
\nSQL> select owner,view_name,container_data,text from dba_views where view_name in ('CDB_HIST_SNAPSHOT','DBA_HIST_SNAPSHOT');\n \nOWNER  VIEW_NAME                      C TEXT\n------ ------------------------------ - --------------------------------------------------------------------------------\nSYS    DBA_HIST_SNAPSHOT              N select \"SNAP_ID\",\"DBID\",\"INSTANCE_NUMBER\",\"STARTUP_TIME\",\"BEGIN_INTERVAL_TIME\",\"\n                                        END_INTERVAL_TIME\",\"FLUSH_ELAPSED\",\"SNAP_LEVEL\",\"ERROR_COUNT\",\"SNAP_FLAG\",\"SNAP_\n                                        TIMEZONE\",\"CON_ID\" from AWR_ROOT_SNAPSHOT\n \nSYS    CDB_HIST_SNAPSHOT              Y SELECT k.\"SNAP_ID\",k.\"DBID\",k.\"INSTANCE_NUMBER\",k.\"STARTUP_TIME\",k.\"BEGIN_INTERV\n                                        AL_TIME\",k.\"END_INTERVAL_TIME\",k.\"FLUSH_ELAPSED\",k.\"SNAP_LEVEL\",k.\"ERROR_COUNT\",\n                                        k.\"SNAP_FLAG\",k.\"SNAP_TIMEZONE\",k.\"CON_ID\", k.CON$NAME, k.CDB$NAME FROM CONTAINE\n                                        RS(\"SYS\".\"AWR_PDB_SNAPSHOT\") k\n
\n

The DBA_HIST_SNAPSHOT is a simple one view on AWR_ROOT_SNAPSHOT which, as we have seen above, always show snapshots from CDB:

\n
\nSQL> alter session set container=CDB$ROOT;\nSession altered.\n \nSQL> select dbid,count(*) from DBA_HIST_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n&nbsp\nSQL> alter session set container=PDB1;\nSession altered.\n \nSQL> select dbid,count(*) from DBA_HIST_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n 904475458         91\n
\n

Then CDB_HIST_SNAPSHOT reads AWR_PDB_SNAPSHOT which show current container snapshots. But this view is a COMMON DATA one, with the CONTAINER() function. This means that from CDB$ROOT when executed with a common user data from all open containers will be retrieved:

\n
\nSQL> alter session set container=CDB$ROOT;\nSession altered.\n \nSQL> select dbid,count(*) from CDB_HIST_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n2623271973         79\n 904475458         91\n
\n

However, from a PDB you cannot see anything else:

\n
\nSQL> alter session set container=PDB1;\nSession altered.\n \nSQL> select dbid,count(*) from CDB_HIST_SNAPSHOT group by dbid;\n \n      DBID   COUNT(*)\n---------- ----------\n2623271973         79\n
\n

So what?

\n

Multitenant adds a new dimension in the dictionary views and we must be aware of that. However, compatibility is still there. The scripts that we used to run to query DBA_HIST views should still work. Don’t forget to always join on DBID and INSTANCE_NUMBER in addition to SNAP_ID so that your scripts are still working in RAC, and cross containers.
\nIn 12.2 you can do the same for your application: used metadata links, data links, and common views for your tables. But remember to keep it simple…

\n", "protected": false } }