Oracle segment advisor, how to deal with row link row migration, reduce high water level

Oracle Yes 3 A background program that runs regularly , Consultant Duan suggested 、SQL Statement diagnosis 、 collect Statistics , The recommendation of the consultant is to analyze whether the distribution of table data in the data block is reasonable , Such as whether to generate row links 、 Line migration 、 Whether the high water level is reasonable .

Check whether consultant Duan suggests enabling

SELECT client_name ,status ,consumer_group
FROM dba_autotask_client
ORDER BY client_name;

see auto space advisor The status of this line

Enable the section consultant's suggestion

-- Enable 
BEGIN
  DBMS_AUTO_TASK_ADMIN.ENABLE(
  client_name => 'sql tuning advisor',
  operation => NULL,
  window_name => NULL);
END;
/
-- see 
SELECT window_name,TO_CHAR(window_next_time,'YYYY-MM-DD HH24:MI:SS')
,sql_tune_advisor
FROM dba_autotask_window_clients;

Check the content suggested by the consultant

SELECT
'Segment Advice --------------------------'|| chr(10) ||
'TABLESPACE_NAME : ' || tablespace_name || chr(10) ||
'SEGMENT_OWNER : ' || segment_owner || chr(10) ||
'SEGMENT_NAME : ' || segment_name || chr(10) ||
'ALLOCATED_SPACE : ' || allocated_space || chr(10) ||
'RECLAIMABLE_SPACE: ' || reclaimable_space || chr(10) ||
'RECOMMENDATIONS : ' || recommendations || chr(10) ||
'SOLUTION 1 : ' || c1 || chr(10) ||
'SOLUTION 2 : ' || c2 || chr(10) ||
'SOLUTION 3 : ' || c3 Advice
FROM
TABLE(dbms_space.asa_recommendations('FALSE', 'FALSE', 'FALSE'));

select
'Task Name : ' || f.task_name || chr(10) ||
'Start Run Time : ' || TO_CHAR(execution_start, 'dd-mon-yy hh24:mi') || chr (10) ||
'Segment Name : ' || o.attr2 || chr(10) ||
'Segment Type : ' || o.type || chr(10) ||
'Partition Name : ' || o.attr3 || chr(10) ||
'Message : ' || f.message || chr(10) ||
'More Info : ' || f.more_info || chr(10) ||
'------------------------------------------------------' Advice
FROM dba_advisor_findings f
,dba_advisor_objects o
,dba_advisor_executions e
WHERE o.task_id = f.task_id
AND o.object_id = f.object_id
AND f.task_id = e.task_id
AND e. execution_start > sysdate - 1
AND e.advisor_name = 'Segment Advisor'
ORDER BY f.task_name;

What is a line link

Row linking is due to its large amount of data （ Initial or later updated ）, As a result, a row of data needs to span multiple data blocks , This is the line link .

What is row migration

A row data block is smaller initially or after being updated , It will be put into other data blocks with space , Only one pointer is reserved in the original data block , Point to the data block where the data is stored , This is row migration .

What are the disadvantages of row linking and row migration

When reading data, redundant I/O.

How to handle row linking and row migration

1. Move

1. Move table alter table xxx move;
2. Rebuild all indexes of the table

it is to be noted that , During this period, this table cannot have transactions .

2. Data migration

1. Run an analysis script to analyze the linked data
2. Insert the data generated by row linking and row migration into the temporary table
3. Delete the data of row link and row migration generated by the original table
4. Insert the data of the temporary table into the original table

3. Use the data pump to import and export the reconstruction table

What is high water level

High water level is the dividing line between unused data blocks and used data blocks , When querying data, start from the high water mark and look down .

How to lower the high water level

Yes 4 Medium method ：

1. Contractile table

1. Enable row migration alter table emp enable row movement
2. Execute shrink alter table emp shrink space;
3. Rebuild index

2.truncate surface

3. Move table （ Need to re index ）

4. Use the data pump to export the table , Delete table , Re import