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How to do session and v$session instructions

2025-01-16 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Database >

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In this issue, the editor will bring you instructions on how to carry out session and v$session. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

1. Preface

V$session and v$process views are the most commonly used views for database management to understand system performance and analyze system reasons, so as a non-rookie DBA administrator, you need to have a full understanding of these two views.

2. Concept

You must first understand what session is: generally speaking, session is a context between the two parties from the beginning of the communication to the end of the communication. This context is a piece of memory on the server side: it records the client machine of this connection, which application is passed, which user is logging in, and so on. Session and connection are established at the same time, and they are different levels of description of the same thing. To put it simply, connection is the physical communication link between the client and the server, and session is the logical communication interaction between the user and the server.

The prerequisite for a user in oracle to log on to the oracle server is that the user has the "create session" permission of oracle. Oracle allows the same user to establish multiple connections to the server on the same client, as can be seen in oracle's view V$session [select * from sessions;]. Each session represents an interaction between the user and the server. Just like two countries can have a lot of negotiations at the same time, economic, environmental and so on. The closure of negotiations on the economy will not affect the progress of environmental negotiations. The background process PMON will test the user's connection status every once in a while. If the connection has been disconnected, PMON will clean up the site and release related resources.

1. Log in to oracle with sqlplus

This scenario is easy to understand, where a connection corresponds to a session.

two。 Other client tools log in to oracle

For example, pl/sql developer logs in to oracle. Pl/sql developer can set whether each window shares the same session. If you want to debug a stored procedure or function in the debug window, you must set it to a shared session. If set to non-shared, each time an operation window is opened, pl/sql developer uses the account and password initially entered to establish a new connection and session.

3. IIS logs in to oracle with a program

In this case, IIS is actually logging into oracle. The establishment of connection and session is related to the iis mechanism.

"for Oracle, the safe number of Sessions should be Sessions = (IIS process number) * (min pool size)."

IIS processes: in IIS6.0, a new process isolation mode is used to respond to user requests, and in IIS Manager, you can set the maximum number of processes in the application pool. For new WEB application requests, the IIS process manager starts multiple W3wp.exe to respond.

4. Java configure connection pooling

When you apply the script to configure java, you can configure the corresponding number of session, so that the corresponding session is assigned by default when the application is connected, and these session will not be cleared by PMON regardless of whether there is a connection or not, reducing database overhead.

3. Description of v$session view

All the session of the database provides the corresponding view v$session, which provides a window of query and management for all dba, so it is necessary to know the relevant information of v$session.

Column

Datatype

Description

Description

SADDR

RAW (4 | 8)

Session address

SID

NUMBER

Session identifier

Use these two values to determine the unique session

SERIAL#

NUMBER

Session serial number. Used to uniquely identify a session's objects. Guarantees that session-level commands are applied to the correct session objects if the session ends and another session begins with the same session ID.

AUDSID

NUMBER

Auditing session ID

If AUDSID=0, then it is an internally generated SYS session.

If AUDSID=UB4MAX (4294967295), then it is a direct SYS session.

PADDR

RAW (4 | 8)

Address of the process that owns the session

Process address, the addr field associated with the v$process

USER#

NUMBER

Oracle user identifier

Associate with dba_users

USERNAME

VARCHAR2 (30)

Oracle username

Same as dba_users

COMMAND

NUMBER

Command in progress (last statement parsed).

Session is executing sql id,1 on behalf of create table,3 on behalf of select

You can find the command name for any value n returned in thisCOMMAND column by running this SQL query:

SELECT command_name

FROM v$sqlcommand

WHERE command_type = n

A value of 0 in this COMMAND column means the command is not recorded in V$SESSION.

OWNERID

NUMBER

Identifier of the user who owns the migratable session; the column contents are invalid if the value is 2147483644

For operations using Parallel Slaves, interpret this value as a 4-byte value. The low-order 2 bytes represent the session number and the high-order bytes represent the instance ID of the query coordinator.

TADDR

VARCHAR2 (8)

Address of the transaction state object

The current transaction address. Can be used to associate addr fields in v$transaction

LOCKWAIT

VARCHAR2 (8)

Address of the lock the session is waiting for; NULL if none

You can use this field to query information about the lock you are currently waiting for. Sid + lockwait corresponds to sid + kaddr in v$loc.

STATUS

VARCHAR2 (8)

Status of the session:

Used to determine the status of session. Active: executing SQL statement. Inactive: wait for the operation. Killed: marked to kill

ACTIVE-Session currently executing SQL

INACTIVE-Session which is inactive and either has no configured limits or has not yet exceeded the configured limits

KILLED-Session marked to be killed

CACHED-Session temporarily cached for use by Oracle*XA

SNIPED-An inactive session that has exceeded some configured limits (for example, resource limits specified for the resource manager consumer group or idle_time specified in the user's profile). Such sessions will not be allowed to become active again.

SERVER

VARCHAR2 (9)

Server type:

Service type (general dedicated type)

DEDICATED

SHARED

PSEUDO

POOLED

NONE

SCHEMA#

NUMBER

Schema user identifier

Consistent with USER#

SCHEMANAME

VARCHAR2 (30)

Schema user name

Consistent with USERNAME

OSUSER

VARCHAR2 (30)

Operating system client user name

Client operating system user name

PROCESS

VARCHAR2 (24)

Operating system client process ID

Client process id

MACHINE

VARCHAR2 (64)

Operating system machine name

Client machine name

PORT

NUMBER

Client port number

Port number of the client

TERMINAL

VARCHAR2 (30)

Operating system terminal name

Terminal name executed by the client

PROGRAM

VARCHAR2 (48)

Operating system program name

Client application

TYPE

VARCHAR2 (10)

Session type

User process or background process. Generally speaking, background process cannot KILL

SQL_ADDRESS

RAW (4 | 8)

Used with SQL_HASH_VALUE to identify the SQL statement that is currently being executed

SQL_HASH_VALUE

NUMBER

Used with SQL_ADDRESS to identify the SQL statement that is currently being executed

SQL_ID

VARCHAR2 (13)

SQL identifier of the SQL statement that is currently being executed

The SQL statement that is currently executed, associated with v$sql

SQL_CHILD_NUMBER

NUMBER

Child number of the SQL statement that is currently being executed

SQL_EXEC_START

DATE

Time when the execution of the SQL currently executed by this session started; NULL if SQL_ID is NULL

The start time of the current sql

SQL_EXEC_ID

NUMBER

SQL execution identifier; NULL if SQL_ID is NULL or if the execution of that SQL has not yet started (see V$SQL_MONITOR)

PREV_SQL_ADDR

RAW (4 | 8)

Used with PREV_HASH_VALUE to identify the last SQL statement executed

PREV_HASH_VALUE

NUMBER

Used with SQL_HASH_VALUE to identify the last SQL statement executed

PREV_SQL_ID

VARCHAR2 (13)

SQL identifier of the last SQL statement executed

The SQL statement that has just been executed. Query the corresponding SQL statement from v$sql.

PREV_CHILD_NUMBER

NUMBER

Child number of the last SQL statement executed

PREV_EXEC_START

DATE

SQL execution start of the last executed SQL statement

PREV_EXEC_ID

NUMBER

SQL execution identifier of the last executed SQL statement

PLSQL_ENTRY_OBJECT_ID

NUMBER

Object ID of the top-most PL/SQL subprogram on the stack; 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; NULL if there is no PL/SQL subprogram on the stack

PLSQL_OBJECT_ID

NUMBER

Object ID of the currently executing PL/SQL subprogram; NULL if executing SQL

PLSQL_SUBPROGRAM_ID

NUMBER

Subprogram ID of the currently executing PL/SQL object; NULL if executing SQL

MODULE

VARCHAR2 (48)

Name of the currently executing module as set by calling theDBMS_APPLICATION_INFO.SET_MODULE procedure

MODULE_HASH

NUMBER

Hash value of the MODULE column

ACTIONFootref 1

VARCHAR2 (32)

Name of the currently executing action as set by calling theDBMS_APPLICATION_INFO.SET_ACTION procedure

ACTION_HASH

NUMBER

Hash value of the ACTION column

CLIENT_INFO

VARCHAR2 (64)

Information set by the DBMS_APPLICATION_INFO.SET_CLIENT_INFOprocedure

FIXED_TABLE_SEQUENCE

NUMBER

This contains a number that increases every time the session completes a call to the database and there has been an intervening select from a dynamic performance table. This column can be used by performance monitors to monitor statistics in the database. Each time the performance monitor looks at the database, it only needs to look at sessions that are currently active or have a higher value in this column than the highest value that the performance monitor saw the last time. All the other sessions have been idle since the last time the performance monitor looked at the database.

ROW_WAIT_OBJ#

NUMBER

Object ID for the table containing the row specified in ROW_WAIT_ROW#

ROW_WAIT_FILE#

NUMBER

Identifier for the datafile containing the row specified inROW_WAIT_ROW#. This column is valid only if the session is currently waiting for another transaction to commit and the value ofROW_WAIT_OBJ# is not-1.

ROW_WAIT_BLOCK#

NUMBER

Identifier for the block containing the row specified in ROW_WAIT_ROW#. This column is valid only if the session is currently waiting for another transaction to commit and the value of ROW_WAIT_OBJ# is not-1.

ROW_WAIT_ROW#

NUMBER

Current row being locked. This column is valid only if the session is currently waiting for another transaction to commit and the value ofROW_WAIT_OBJ# is not-1.

TOP_LEVEL_CALL#

NUMBER

Oracle top level call number

LOGON_TIME

DATE

Time of logon

LAST_CALL_ET

NUMBER

If the session STATUS is currently ACTIVE, then the value represents the elapsed time (in seconds) since the session has become active.

If the session STATUS is currently INACTIVE, then the value represents the elapsed time (in seconds) since the session has become inactive.

PDML_ENABLED

VARCHAR2 (3)

This column has been replaced by the PDML_STATUS column

FAILOVER_TYPE

VARCHAR2 (13)

Indicates whether and to what extent transparent application failover (TAF) is enabled for the session:

NONE-Failover is disabled for this session

SESSION-Client is able to fail over its session following a disconnect

SELECT-Client is able to fail over queries in progress as well

See Also:

Oracle Database Concepts for more information on TAF

Oracle Database Net Services Administrator's Guide for information on configuring TAF

FAILOVER_METHOD

VARCHAR2 (10)

Indicates the transparent application failover method for the session:

NONE-Failover is disabled for this session

BASIC-Client itself reconnects following a disconnect

PRECONNECT-Backup instance can support all connections from every instance for which it is backed up

FAILED_OVER

VARCHAR2 (3)

Indicates whether the session is running in failover mode and failover has occurred (YES) or not (NO)

RESOURCE_CONSUMER_GROUP

VARCHAR2 (32)

Name of the session's current resource consumer group

PDML_STATUS

VARCHAR2 (8)

If ENABLED, the session is in a PARALLEL DML enabled mode. If DISABLED,PARALLEL DML enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLEL DML.

PDDL_STATUS

VARCHAR2 (8)

If ENABLED, the session is in a PARALLEL DDL enabled mode. If DISABLED,PARALLEL DDL enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLEL DDL.

PQ_STATUS

VARCHAR2 (8)

If ENABLED, the session is in a PARALLEL QUERY enabled mode. IfDISABLED, PARALLEL QUERY enabled mode is not supported for the session. If FORCED, the session has been altered to force PARALLELQUERY.

CURRENT_QUEUE_DURATION

NUMBER

If queued (1), the current amount of time the session has been queued. If not currently queued, the value is 0.

CLIENT_IDENTIFIER

VARCHAR2 (64)

Client identifier of the session

BLOCKING_SESSION_STATUS

VARCHAR2 (11)

This column provides details on whether there is a blocking session:

VALID-there is a blocking session, and it is identified in theBLOCKING_INSTANCE and BLOCKING_SESSION columns

NO HOLDER-there is no session blocking this session

NOT IN WAIT-this session is not in a wait

UNKNOWN-the blocking session is unknown

BLOCKING_INSTANCE

NUMBER

Instance identifier of the blocking session. This column is valid only ifBLOCKING_SESSION_STATUS has the value VALID.

BLOCKING_SESSION

NUMBER

Session identifier of the blocking session. This column is valid only ifBLOCKING_SESSION_STATUS has the value VALID.

FINAL_BLOCKING_SESSION_STATUS

VARCHAR2 (11)

The final blocking session is the final element in the wait chain constructed by following the sessions that are blocked by one another starting with this session. In the case of a cyclical wait chain, one of the sessions in the wait chain will be chosen as the final blocker.

This column provides details on whether there is a final blocking session:

VALID-there is a final blocking session and it is identified in theFINAL_BLOCKING_INSTANCE and FINAL_BLOCKING_SESSION columns

NO HOLDER-there is no session blocking this session

NOT IN WAIT-this session is not in a wait

UNKNOWN-the final blocking session is unknown

FINAL_BLOCKING_INSTANCE

NUMBER

Instance identifier of the final blocking session. This column is valid only ifFINAL_BLOCKING_SESSION_STATUS has the value VALID.

FINAL_BLOCKING_SESSION

NUMBER

Session identifier of the blocking session. This column is valid only ifFINAL_BLOCKING_SESSION_STATUS has the value VALID.

SEQ#

NUMBER

A number that uniquely identifies the current or last wait (incremented for each wait)

EVENT#

NUMBER

Event number

The number of the waiting event is associated with v$session_wait

EVENT

VARCHAR2 (64)

Resource or event for which the session is waiting

The interpretation of waiting events is associated with v$session_wait

See Also: Appendix C, "Oracle Wait Events"

P1TEXT

VARCHAR2 (64)

Description of the first wait event parameter

FILE_ID,BLOCK_ID,BLOCKS corresponding to DBA_EXTENTS

P1

NUMBER

First wait event parameter (in decimal)

P1RAW

RAW (8)

First wait event parameter (in hexadecimal) Foot 2

P2TEXT

VARCHAR2 (64)

Description of the second wait event parameter

P2

NUMBER

Second wait event parameter (in decimal)

P2RAW

RAW (8)

Second wait event parameter (in hexadecimal) Footref 2

P3TEXT

VARCHAR2 (64)

Description of the third wait event parameter

P3

NUMBER

Third wait event parameter (in decimal)

P3RAW

RAW (8)

Third wait event parameter (in hexadecimal) Footref 2

WAIT_CLASS_ID

NUMBER

Identifier of the class of the wait event

WAIT_CLASS#

NUMBER

Number of the class of the wait event

WAIT_CLASS

VARCHAR2 (64)

Name of the class of the wait event

WAIT_TIME

NUMBER

If the session is currently waiting, then the value is 0. If the session is not in a wait, then the value is as follows:

> 0-Value is the duration of the last wait in hundredths of a second

-1-Duration of the last wait was less than a hundredth of a second

-2-Parameter TIMED_STATISTICS was set to false

This column has been deprecated in favor of the columnsWAIT_TIME_MICRO and STATE.

SECONDS_IN_WAIT

NUMBER

If the session is currently waiting, then the value is the amount of time waited for the current wait. If the session is not in a wait, then the value is the amount of time since the start of the last wait.

This column has been deprecated in favor of the columnsWAIT_TIME_MICRO and TIME_SINCE_LAST_WAIT_MICRO.

STATE

VARCHAR2 (19)

Wait state:

WAITING-Session is currently waiting

The current session is waiting

WAITED UNKNOWN TIME-Duration of the last wait is unknown; this is the value when the parameter TIMED_STATISTICS is set to false

WAITED SHORT TIME-Last wait was less than a hundredth of a second

WAITED KNOWN TIME-Duration of the last wait is specified in theWAIT_TIME column

WAIT_TIME_MICRO

NUMBER

Amount of time waited (in microseconds). If the session is currently waiting, then the value is the time spent in the current wait. If the session is currently not in a wait, then the value is the amount of time waited in the last wait.

TIME_REMAINING_MICRO

NUMBER

Value is interpreted as follows:

> 0-Amount of time remaining for the current wait (in microseconds)

0-Current wait has timed out

-1-Session can indefinitely wait in the current wait

NULL-Session is not currently waiting

TIME_SINCE_LAST_WAIT_MICRO

NUMBER

Time elapsed since the end of the last wait (in microseconds). If the session is currently in a wait, then the value is 0.

SERVICE_NAME

VARCHAR2 (64)

Service name of the session

SQL_TRACE

VARCHAR2 (8)

Indicates whether SQL tracing is enabled (ENABLED) or disabled (DISABLED)

Whether to turn on tracking

SQL_TRACE_WAITS

VARCHAR2 (5)

Indicates whether wait tracing is enabled (TRUE) or not (FALSE)

SQL_TRACE_BINDS

VARCHAR2 (5)

Indicates whether bind tracing is enabled (TRUE) or not (FALSE)

SQL_TRACE_PLAN_STATS

VARCHAR2 (10)

Frequency at which row source statistics are dumped in the trace files for each cursor:

Never

First_execution

All_executions

SESSION_EDITION_ID

NUMBER

Shows the value that, in the session, would be reported bysys_context ('USERENV',' SESSION_EDITION_ID')

CREATOR_ADDR

RAW (4 | 8)

Address of the creating process or circuit

CREATOR_SERIAL#

NUMBER

Serial number of the creating process or circuit

ECID

VARCHAR2 (64)

Execution context identifier (sent by Application Server)

The above are just annotations of commonly used fields. If you miss them, please add them, and follow up with the deepening of the work.

4. The role of v$session in practical work.

4.1 query the session information of locked objects:

SELECT OBJECT_NAME, MACHINE, S.SID, S.SERIAL#

FROM GV$LOCKED_OBJECT L, DBA_OBJECTS O, GV$SESSION S

WHERE L.OBJECT_ID = O.OBJECT_ID AND L.SESSION_ID = S.SID

4.2 View the statements executed in the current session and session-related information:

SELECT A.SID, A.SERIAL#, A.USERNAME, A.TERMINAL, A.PROGRAM, S.SQL_TEXT

FROM V$SESSION A, V$SQLAREA S WHERE A.SQL_ADDRESS = S.ADDRESS (+)

AND A.SQL_HASH_VALUE = S.HASH_VALUE (+) ORDER BY A.USERNAME, A.SID

4.3 Kill the conversation:

ALTER SYSTEM KILL SESSION 'SID, # SERIAL'; (note that the current session tpye cannot be background)

The above is the editor for you to share how to carry out session and v$session explained, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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