New feature of Oracle 19C: automatic DML redirection of ADG, enhanced read-write separation -- ADG_ REDIRECT_ DML

Oracle 19c New characteristics ：ADG Automatic DML Redirection enhances read-write separation --ADG_REDIRECT_DML

Oracle 19c One of the new features ,adg Automatic dml Redirect . Is in the ADG In the environment , Connect to standby Database execution dml.

This feature is available in 18c As an implicit parameter _enable_proxy_adg_redirect Adjusted ,

But in 19c in , Through explicit parameters ADG_REDIRECT_DML Parameter adjustment .

SQL> show parameter adg_redirect_dml;

NAME      TYPE VALUE

------------------------------------ ----------- ------------------------------

adg_redirect_dml      boolean FALSE

The default is false

stay primary and standby All open

SQL> alter system set adg_redirect_dml = true scope = both sid = '*';

After the test, it was found that dblink The way to primay perform dml, So we need to monitor standby Of 2pc It's abnormal .

Reference resources :

​ ​https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/ADG_REDIRECT_DML.html#GUID-AC98F026-33BE-41FE-8F2F-EFA296723AD8​​

​ ​https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/release-changes.html#GUID-509A6343-5882-4260-BAD0-DC6B2BDC8301​​

explain

stay 19c In the version ,ADG Backup library support in DML operation , The principle is ： It's through DML Redirect to the main library to execute , Then the standby application DML Change data , So far, the standby database is completed DML operation .

notes ： Avoid executing too much... On the standby database DML operation , It is actually executed on the main library .

I won't support it XA In the transaction DML operation .

To configure

Automatic redirection DML Operations support session level and system level , Session level overrides system level configuration .

Enable... On all standby databases DML Redirect

Will initialize parameters ADG_REDIRECT_DML Set to true

ALTER SYSTEM SET ADG_REDIRECT_DML=true SCOPE=BOTH;

The current session is enabled DML Redirect

ALTER SESSION ENABLE ADG_REDIRECT_DML;

Specific examples

Conversation level DML Redirect

Confirm the current database role

SQL>  select open_mode,database_role from v$database;

OPEN_MODE                                DATABASE_ROLE

---------------------------------------- --------------------------------

READ ONLY WITH APPLY                     PHYSICAL STANDBY

Enable session level... On the standby DML Redirect

SQL> conn system/oracle   -- Not sys user

Connected.

SQL> ALTER SESSION ENABLE ADG_REDIRECT_DML;

Session altered.

Confirm table data

  SQL> select * from test;

  no rows selected

Execute... On the standby database DML operation

SQL> insert into test values(1);

1 row created.

SQL> select * from test;

      ID

  ----------

       1

Be careful ： I won't support it sys User session enable ：ORA-16397: statement redirection from Oracle Active Data Guard standby database to primary database failed

Possible causes of the error ：

[[email protected]_p admin]$ oerr ORA 16397

16397, 00000, "statement redirection from Oracle Active Data Guard standby database to primary database failed"

// *Cause:  The statement redirection failed because of one of the following reasons:

//          1. The primary database connect string was not established.

//          2. The primary database could not be reached.

//          3. The undo-mode or incarnation were not the same.

//          4. The current user and logged-in user were not the same.

//          5. Redirecting CREATE TABLE AS SELECT (CTAS) of the global temporary

//             table was not supported.

//          6. Redirecting PL/SQL execution having bind variable was not supported.

// *Action: Run the statement after fixing the condition that caused the failure.

System level enable DML Redirect

see ADG_REDIRECT_DML Parameter values

SQL> SHOW PARAMETER ADG_REDIRECT_DML;

NAME                                 TYPE

------------------------------------ ----------------------

VALUE

------------------------------

adg_redirect_dml                     boolean

FALSE

Set to... On the standby database true

SQL> ALTER SYSTEM SET ADG_REDIRECT_DML=true SCOPE=BOTH;

System altered.

perform DML

 SQL> conn system/oracle

 Connected.

 SQL> insert into system.test values(2);

 1 row created.

 SQL> COMMIT;

 Commit complete.

Validation data

 SQL> select * from system.test;

         ID

 ----------

         1

         2

That's about ADG Medium backup Library DML Redirect feature test ,

In the previous article 《 ​ ​Oracle 19c A list of ten new features ​​》 in , We have mentioned Oracle 19c An important enhancement of , Namely ADG Automatic DML forward ：

The function of this new feature is ： Will be sent to ADG Upper DML operation , Automatically forward to the main library for execution , Then, it is transferred to the backup database real-time application through the main database log , It's guaranteed ACID Under the premise of , Greatly enhance the practicality of the backup library , This is known as DML Redirection .

In fact, this feature is Oracle 18c We have already provided , So we don't have to wait for 19c You can experience this feature .

In both versions , The only difference is ：

stay 18c in , This feature is through implicit parameters _enable_proxy_adg_redirect To enable this feature , This means that the feature tends to be internal ;

stay 19c in , Explicit parameters ADG_REDIRECT_DML Parameters control the switch of this feature , It shows that this feature becomes external and mature ;

Take a look at the test , Experience the convenience of this new feature . First, create a test table in the main database , Insert test data ：

[[email protected]]$  export ORACLE_SID=DB18C  

[[email protected]]$ sqlplus / as sysdba

Connected to:

Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production

SQL> create user eygle identified by eygle;

User created.

SQL> grant connect,resource,dba to eygle;

Grant succeeded.

SQL> connect eygle/eygle

Connected.

SQL> create table enmotech (id number,name varchar2(20));

Table created.

SQL> insert into enmotech values(1,'EYGLE');

1 row created.

SQL> commit;

Commit complete.

SQL> select open_mode from v$database;

OPEN_MODE

--------------------

READ WRITE

Next, after setting the parameters in the standby database , It can be executed against the table DML Operation , Note that the backup library needs to be placed in Real time application status ：

[[email protected]]$ export ORACLE_SID=DB18C_S

[[email protected]]$ sqlplus eygle/eygle

Connected to:

Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production

SQL> select open_mode from v$database;

OPEN_MODE

--------------------

READ ONLY WITH APPLY

SQL> select * from enmotech;

ID NAME

---------- --------------------

1 EYGLE

SQL> alter session set "_enable_proxy_adg_redirect"=true;

Session altered.

SQL> show parameter redirect

NAME      TYPE VALUE

------------------------------------ ----------- ------------------------------

_adg_redirect_flags      integer 1

_enable_proxy_adg_redirect      boolean TRUE

-- Trace is enabled here , Can be analyzed ADG How redirection works

SQL> alter session set events '10046 trace name context forever ,level 12';

Session altered.

-- Here DML The operation can be carried out smoothly

SQL> insert into enmotech values(2,'YANGTINGKUN');

1 row created.

SQL> select * from enmotech;

ID NAME

---------- --------------------

1 EYGLE

2 YANGTINGKUN

SQL> commit;

Commit complete.

In the above test , Can be set by 10046 track , To get recursive execution in the background , Study how this feature works .

You can also set the terminal output time , Evaluate redirection latency , My test environment is built on the same host , Basically DML The delay of the operation is 1 About seconds , It's totally acceptable in case of accident ：

SQL> set timing on

SQL> insert into enmotech values(2,'KAMUS');

1 row created.

Elapsed: 00:00:01.05

SQL> select * from enmotech;

ID NAME

---------- --------------------

1 EYGLE

2 YANGTINGKUN

2 KAMUS

Elapsed: 00:00:00.00

SQL> commit;

Commit complete.

Elapsed: 00:00:01.05

Through the tracking log in the background , You can see ,DML The operation is through DB Link To redirect to the main library , This DB Link It's internal , Under the normal configuration of service name and so on ,Oracle Can automatically complete internal operations , If the configuration is wrong, there will be an error ：

=====================

PARSING IN CURSOR #139880746795960 len=44 dep=0 uid=107 oct=2 lid=107 tim=45368825051292 hv=3193100945 ad='674870e8' sqlid='3bg4wy2z55qnj'

insert into enmotech values(2,'YANGTINGKUN')

END OF STMT

PARSE #139880746795960:c=44993,e=1721825,p=1,cr=28,cu=6,mis=1,r=0,dep=0,og=1,plh=0

WAIT #139880746795960: nam='SQL*Net message to dblink' ela= 2 

WAIT #139880746795960: nam='SQL*Net message from dblink' ela= 1164 

EXEC #139880746795960:c=1000,e=1297,p=0,cr=0,cu=0,mis=0,r=1,dep=0,og=1,plh=0

WAIT #139880746795960: nam='SQL*Net message to dblink' ela= 1 

WAIT #139880746795960: nam='SQL*Net vector data to dblink' ela= 82 

WAIT #139880746795960: nam='SQL*Net message from dblink' ela= 1280 

*** 2019-01-10T21:08:37.292860+08:00

WAIT #139880746795960: nam='standby query scn advance' ela= 850283 

WAIT #139880746795960: nam='PGA memory operation' ela= 98 p1=0 p2=0 

WAIT #139880746795960: nam='SQL*Net message to client' ela= 2 d

=====================

PARSING IN CURSOR #139880746795960 len=6 dep=0 uid=107 oct=44 lid=107 tim=45368881823728 hv=3480936638 ad='0' sqlid='23wm3kz7rps5y'

commit

END OF STMT

PARSE #139880746795960:c=0,e=150,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,plh=0

XCTEND rlbk=0, rd_only=1, tim=45368881823795

WAIT #139880746795960: nam='SQL*Net message to dblink' ela= 2 

WAIT #139880746795960: nam='SQL*Net message from dblink' ela= 1598 

*** 2019-01-10T21:09:34.259699+08:00

WAIT #139880746795960: nam='standby query scn advance' ela= 1045191 

EXEC #139880746795960:c=1000,e=1047570,p=0,cr=0,cu=4,mis=0,r=0,dep=0,og=0,plh=0

WAIT #139880746795960: nam='SQL*Net message to client' ela= 3 

In addition to the regular tables ,Oracle It also supports the creation of global temporary tables in the standby database , stay 19c in , Implied parameters  _alter_adg_redirect_behavior Can be used to define the level of redirection allowed , For example, when setting  disallow_gtt Redirection of global temporary tables will not be allowed .

ADG in DML Another problem with redirecting new features , Later deployment ADG when , We must pay attention to the safety control of the backup warehouse , Otherwise, it will be distributed to the backup database DML May damage the consistency of the main library .

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