DBA_Hist_Active_Sess_History | Active Session History (ASH) in Oracle

Mehmet Salih Deveci

3 years ago

I will explain DBA_Hist_Active_Sess_History | Active Session History (ASH) in Oracle in this post.

DBA_Hist_Active_Sess_History | Active Session History (ASH) in Oracle

dba_hist_active_sess_history view is one of the most important Oracle views that displays history of the contents of the in-memory active session history of recent system activity. It contains snapshots of V$ACTIVE_SESSION_HISTORY

dba_hist_active_sess_history columns are as follows.

Column	Datatype	NULL	Description
`SNAP_ID`	`NUMBER`	`NOT NULL`	Unique snapshot ID
`DBID`	`NUMBER`	`NOT NULL`	Database ID for the snapshot
`INSTANCE_NUMBER`	`NUMBER`	`NOT NULL`	Instance number for the snapshot
`SAMPLE_ID`	`NUMBER`	`NOT NULL`	ID of the sample
`SAMPLE_TIME`	`TIMESTAMP(3)`	`NOT NULL`	Time of the sample
`SESSION_ID`	`NUMBER`	`NOT NULL`	Session identifier
`SESSION_SERIAL#`	`NUMBER`		Session serial number (used to uniquely identify a session’s objects)
`SESSION_TYPE`	`VARCHAR2(10)`		Session type: `FOREGROUND` `BACKGROUND`
`FLAGS`	`NUMBER`		Reserved for future use
`USER_ID`	`NUMBER`		Oracle user identifier
`SQL_ID`	`VARCHAR2(13)`		SQL identifier of the SQL statement that is currently being executed
`IS_SQLID_CURRENT`	`VARCHAR2(1)`		Indicates whether the SQL identifier in the `SQL_ID` column is being executed (`Y`) or not (`N`)
`SQL_CHILD_NUMBER`	`NUMBER`		Child number of the SQL statement that is currently being executed
`SQL_OPCODE`	`NUMBER`		Indicates what phase of operation the SQL statement is in
`SQL_OPNAME`	`VARCHAR2(64)`		SQL command name
`FORCE_MATCHING_SIGNATURE`	`NUMBER`		Signature used when the `CURSOR_SHARING` parameter is set to `FORCE`
`TOP_LEVEL_SQL_ID`	`VARCHAR2(13)`		SQL identifier of the top level SQL statement
`TOP_LEVEL_SQL_OPCODE`	`NUMBER`		Indicates what phase of operation the top level SQL statement was in
`SQL_PLAN_HASH_VALUE`	`NUMBER`		Numerical representation of the SQL plan for the cursor
`SQL_FULL_PLAN_HASH_VALUE`	`NUMBER`		Numerical representation of the complete SQL plan for the cursor being executed by this session
`SQL_ADAPTIVE_PLAN_RESOLVED`	`NUMBER`		Indicates whether the SQL plan of the sampled database session is a resolved adaptive plan or not
`SQL_PLAN_LINE_ID`	`NUMBER`		SQL plan line ID
`SQL_PLAN_OPERATION`	`VARCHAR2(64)`		Plan operation name
`SQL_PLAN_OPTIONS`	`VARCHAR2(64)`		Plan operation options
`SQL_EXEC_ID`	`NUMBER`		SQL execution identifier
`SQL_EXEC_START`	`DATE`		Time when the execution of the SQL started
`PLSQL_ENTRY_OBJECT_ID`	`NUMBER`		Object ID of the top-most PL/SQL subprogram on the stack (or NULL if there is no PL/SQL subprogram on the stack)
`PLSQL_ENTRY_SUBPROGRAM_ID`	`NUMBER`		Subprogram ID of the top-most PL/SQL subprogram on the stack (or NULL if there is no PL/SQL subprogram on the stack)
`PLSQL_OBJECT_ID`	`NUMBER`		Object ID of the currently executing PL/SQL subprogram (or NULL if executing SQL)
`PLSQL_SUBPROGRAM_ID`	`NUMBER`		Subprogram ID of the currently executing PL/SQL object (or NULL if executing SQL)
`QC_INSTANCE_ID`	`NUMBER`		Query coordinator instance ID
`QC_SESSION_ID`	`NUMBER`		Query coordinator session ID
`QC_SESSION_SERIAL#`	`NUMBER`		Query coordinator session serial number
`PX_FLAGS`	`NUMBER`		Reserved for internal use
`EVENT`	`VARCHAR2(64)`		If `SESSION_STATE = WAITING`, then the event for which the session was waiting at the time of sampling. If `SESSION_STATE = ON CPU`, then this column will be NULL.
`EVENT_ID`	`NUMBER`		Identifier of the resource or event for which the session is waiting or for which the session last waited
`SEQ#`	`NUMBER`		Sequence number that uniquely identifies the wait (incremented for each wait)
`P1TEXT`	`VARCHAR2(64)`		Text of first additional parameter
`P1`	`NUMBER`		First additional parameter
`P2TEXT`	`VARCHAR2(64)`		Text of second additional parameter
`P2`	`NUMBER`		Second additional parameter
`P3TEXT`	`VARCHAR2(64)`		Text of third additional parameter
`P3`	`NUMBER`		Third additional parameter
`WAIT_CLASS`	`VARCHAR2(64)`		Wait class name of the event for which the session was waiting at the time of sampling. Interpretation is similar to that of the `EVENT` column. Maps to `V$SESSION.WAIT_CLASS`.
`WAIT_CLASS_ID`	`NUMBER`		Wait class identifier of the event for which the session was waiting at the time of sampling. Interpretation is similar to that of the `EVENT` column. Maps to `V$SESSION.WAIT_CLASS_ID`.
`WAIT_TIME`	`NUMBER`		Total wait time (in microseconds) for the event for which the session last waited (`0` if currently waiting)
`SESSION_STATE`	`VARCHAR2(7)`		Session state: `WAITING` `ON` `CPU`
`TIME_WAITED`	`NUMBER`		Time that the current session actually spent waiting for the event (in microseconds). This column is set for waits that were in progress at the time the sample was taken.
`BLOCKING_SESSION_STATUS`	`VARCHAR2(11)`		Status of the blocking session: `VALID` `NO HOLDER` `GLOBAL` `NOT IN WAIT` `UNKNOWN`
`BLOCKING_SESSION`	`NUMBER`		Session identifier of the blocking session. Populated only when the session was waiting for enqueues or a “buffer busy” wait. Maps to `V$SESSION.BLOCKING_SESSION`.
`BLOCKING_SESSION_SERIAL#`	`NUMBER`		Serial number of the blocking session
`BLOCKING_INST_ID`	`NUMBER`		Instance number of the blocker shown in `BLOCKING_SESSION`
`BLOCKING_HANGCHAIN_INFO`	`VARCHAR2(1)`		Indicates whether the information about `BLOCKING_SESSION` comes from the hang chain (`Y`) or not (`N`)
`CURRENT_OBJ#`	`NUMBER`		Object ID of the object that the session is currently referencing. This information is only available if the session was waiting for Application, Cluster, Concurrency, and User I/O wait events. Maps to `V$SESSION.ROW_WAIT_OBJ#`.
`CURRENT_FILE#`	`NUMBER`		File number of the file containing the block that the session is currently referencing. This information is only available if the session was waiting for Cluster, Concurrency, and User I/O wait events. Maps to `V$SESSION.ROW_WAIT_FILE#`.
`CURRENT_BLOCK#`	`NUMBER`		ID of the block that the session is currently referencing
`CURRENT_ROW#`	`NUMBER`		Row identifier that the session is referencing
`TOP_LEVEL_CALL#`	`NUMBER`		Oracle top level call number
`TOP_LEVEL_CALL_NAME`	`VARCHAR2(64)`		Oracle top level call name
`CONSUMER_GROUP_ID`	`NUMBER`		Consumer group ID
`XID`	`RAW(8)`		Transaction ID that the session was working on at the time of sampling. `V$SESSION` does not contain this information.
`REMOTE_INSTANCE#`	`NUMBER`		Remote instance identifier that will serve the block that this session is waiting for. This information is only available if the session was waiting for cluster events.
`TIME_MODEL`	`NUMBER`		Time model information
`IN_CONNECTION_MGMT`	`VARCHAR2(1)`		Indicates whether the session was doing connection management at the time of sampling (`Y`) or not (`N`)
`IN_PARSE`	`VARCHAR2(1)`		Indicates whether the session was parsing at the time of sampling (`Y`) or not (`N`)
`IN_HARD_PARSE`	`VARCHAR2(1)`		Indicates whether the session was hard parsing at the time of sampling (`Y`) or not (`N`)
`IN_SQL_EXECUTION`	`VARCHAR2(1)`		Indicates whether the session was executing SQL statements at the time of sampling (`Y`) or not (`N`)
`IN_PLSQL_EXECUTION`	`VARCHAR2(1)`		Indicates whether the session was executing PL/SQL at the time of sampling (`Y`) or not (`N`)
`IN_PLSQL_RPC`	`VARCHAR2(1)`		Indicates whether the session was executing inbound PL/SQL RPC calls at the time of sampling (`Y`) or not (`N`)
`IN_PLSQL_COMPILATION`	`VARCHAR2(1)`		Indicates whether the session was compiling PL/SQL at the time of sampling (`Y`) or not (`N`)
`IN_JAVA_EXECUTION`	`VARCHAR2(1)`		Indicates whether the session was executing Java at the time of sampling (`Y`) or not (`N`)
`IN_BIND`	`VARCHAR2(1)`		Indicates whether the session was doing bind operations at the time of sampling (`Y`) or not (`N`)
`IN_CURSOR_CLOSE`	`VARCHAR2(1)`		Indicates whether the session was closing a cursor at the time of sampling (`Y`) or not (`N`)
`IN_INMEMORY_QUERY`^Foot 1	`VARCHAR2(1)`		Indicates whether the session was querying the In-Memory Column Store (IM column store) at the time of sampling (`Y`) or not (`N`)
`IN_INMEMORY_POPULATE`^Footref 1	`VARCHAR2(1)`		Indicates whether the session was populating the IM column store at the time of sampling (`Y`) or not (`N`)
`IN_INMEMORY_PREPOPULATE`^Footref 1	`VARCHAR2(1)`		Indicates whether the session was prepopulating the IM column store at the time of sampling (`Y`) or not (`N`)
`IN_INMEMORY_REPOPULATE`^Footref 1	`VARCHAR2(1)`		Indicates whether the session was repopulating the IM column store at the time of sampling (`Y`) or not (`N`)
`IN_INMEMORY_TREPOPULATE`^Footref 1	`VARCHAR2(1)`		Indicates whether the session was trickle repopulating the IM column store at the time of sampling (`Y`) or not (`N`)
`IN_SEQUENCE_LOAD`	`VARCHAR2(1)`		Indicates whether the session is loading in sequence (in sequence load code) (`Y`) or not (`N`)
`CAPTURE_OVERHEAD`	`VARCHAR2(1)`		Indicates whether the session is executing capture code (`Y`) or not (`N`)
`REPLAY_OVERHEAD`	`VARCHAR2(1)`		Indicates whether the session is executing replay code (`Y`) or not (`N`)
`IS_CAPTURED`	`VARCHAR2(1)`		Indicates whether the session is being captured (`Y`) or not (`N`)
`IS_REPLAYED`	`VARCHAR2(1)`		Indicates whether the session is being replayed (`Y`) or not (`N`)
`SERVICE_HASH`	`NUMBER`		Hash that identifies the Service
`PROGRAM`	`VARCHAR2(64)`		Name of the operating system program
`MODULE`	`VARCHAR2(64)`		Name of the currently executing module as set by the `DBMS_APPLICATION_INFO.SET_MODULE` procedure
`ACTION`	`VARCHAR2(64)`		Name of the currently executing action as set by the `DBMS_APPLICATION_INFO.SET_ACTION` procedure
`CLIENT_ID`	`VARCHAR2(64)`		Client identifier of the session
`MACHINE`	`VARCHAR2(64)`		Client’s operating system machine name
`PORT`	`NUMBER`		Client port number
`ECID`	`VARCHAR2(64)`		Execution context identifier (sent by Application Server)
`DBREPLAY_FILE_ID`	`NUMBER`		If the session is being captured or replayed, then `DBREPLAY_FILE_ID` is the file ID for the workload capture or workload replay; otherwise it is NULL.
`DBREPLAY_CALL_COUNTER`	`NUMBER`		If the session is being captured or replayed, then `DBREPLAY_CALL_COUNTER` is the call counter of the user call that is being captured or replayed; otherwise it is NULL.
`TM_DELTA_TIME`	`NUMBER`		Time interval (in microseconds) over which `TM_DELTA_CPU_TIME` and `TM_DELTA_DB_TIME` are accumulated
`TM_DELTA_CPU_TIME`	`NUMBER`		Amount of time this session spent on CPU over the last `TM_DELTA_TIME` microseconds
`TM_DELTA_DB_TIME`	`NUMBER`		Amount of time spent by this session in database calls over the last `TM_DELTA_TIME` microseconds
`DELTA_TIME`	`NUMBER`		Time interval (in microseconds) since the last time this session was sampled or created, over which the next five statistics are accumulated
`DELTA_READ_IO_REQUESTS`	`NUMBER`		Number of read I/O requests made by this session over the last `DELTA_TIME` microseconds
`DELTA_WRITE_IO_REQUESTS`	`NUMBER`		Number of write I/O requests made by this session over the last `DELTA_TIME` microseconds
`DELTA_READ_IO_BYTES`	`NUMBER`		Number of I/O bytes read by this session over the last `DELTA_TIME` microseconds
`DELTA_WRITE_IO_BYTES`	`NUMBER`		Number of I/O bytes written by this session over the last `DELTA_TIME` microseconds
`DELTA_INTERCONNECT_IO_BYTES`	`NUMBER`		Number of I/O bytes sent over the I/O interconnect over the last `DELTA_TIME` microseconds
`PGA_ALLOCATED`	`NUMBER`		Amount of PGA memory (in bytes) consumed by this session at the time this sample was taken
`TEMP_SPACE_ALLOCATED`	`NUMBER`		Amount of TEMP memory (in bytes) consumed by this session at the time this sample was taken
`DBOP_NAME`	`VARCHAR2(64)`		Database operation name. If the type is SQL, the `DBOP_NAME` will be `NULL`.
`DBOP_EXEC_ID`	`NUMBER`		Database operation execution identifier for the current execution. If the type is SQL, the `DBOP_EXEC_ID` will be `NULL`.
`CON_DBID`	`NUMBER`		The database ID of the PDB for the sampled session
`CON_ID`	`NUMBER`		The ID of the container that `CON_DBID` identifies. Possible values include: `0`: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. `1`: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data

You can find the sql statements that are waiting on Gc current block busy and Gc cr block busy wait event using the following script.

select v.sql_text,v.sql_fulltext,sub.* from gv$sql v,
(select sample_time,s.sql_id sql_id, session_state, blocking_session,
owner||'.'||object_name||':'||nvl(subobject_name,'-') obj_name,s.program,s.module,s.machine
from dba_hist_active_sess_history s, dba_objects o
where sample_time between
to_date('02/08/2021  07:30:02','DD/MM/YYYY HH24:MI:SS')
and
to_date('02/08/2021 15:10:02','DD/MM/YYYY HH24:MI:SS')
and event like '%gc%'
and o.data_object_id = s.current_obj#
order by 1 desc) sub where sub.sql_id=v.sql_id;

You can read the following post to read for v$active_session_history view and its details.

V$Active_session_history | Active Session History in Oracle

Do you want to learn Oracle Database Performance Tuning detailed, then read the following articles.

Performance Tuning and SQL Tuning Tutorial in the Oracle Database