Problem with a mass delete operation

Question

Hello,
This questions concerns Oracle v10g.
A table is used to record user login information and other connection related details such as IP address, date of connection, time of login, time of logout etc. from a web-based application.
This table becomes quite large (3 million records+) and is purged once per month of all records older than 3 days old.
The purge is done with a simple delete based on the date of connection CDAT and the column DISX (disconnection=True/False)
DELETE FROM LOGTAB where CDAT < sysdate-3 and DISX='T';The columns CDAT and DISX are indexed. This delete operation can tale up to 10 minutes.
Sporadic problems arise during this delete operation when users connect or disconnect : for those users trying to disconnect, the resulting UPDATE operation on the table currently being deleted seems to hang.
For the users trying to login, there can be a delay (as the INSERT is in suspense). In the worst case all sessions become blocked until the DELETE is finally commited thus rendering any connection impossible for the duration.
There is no conflict between the data being deleted and the data being UPDATED or INSERTED.
The DELETE should only lock the rows that match the WHERE clause, so where is the contention arising from? Could this be index contention?
Is there a better way to manage such mass deletes on such high transaction tables? Partitions?
Thank you in advance.

Answer 1

Have you considered partitioning this table? It would of course depend on whether most queries are looking at the columns you mention, but it would mean you could truncate the partitions older than 3 days ...
create table LOGTAB
(   cdat        date not null,
    disx        varchar2(1) not null,
    col1        varchar2(100)
PARTITION BY RANGE (cdat)
SUBPARTITION BY LIST (disx)
SUBPARTITION TEMPLATE
    (   SUBPARTITION sptn_T VALUES('T'),
        SUBPARTITION sptn_Default VALUES(DEFAULT)
(   PARTITION ptn_20110808 VALUES LESS THAN (TO_DATE('09/08/2011','dd/mm/yyyy')),
    PARTITION ptn_20110809 VALUES LESS THAN (TO_DATE('10/08/2011','dd/mm/yyyy')),
    PARTITION ptn_20110810 VALUES LESS THAN (TO_DATE('11/08/2011','dd/mm/yyyy')),
    PARTITION ptn_20110811 VALUES LESS THAN (TO_DATE('12/08/2011','dd/mm/yyyy')),
    PARTITION ptn_MaxValue VALUES LESS THAN (MAXVALUE)
insert
into
    LOGTAB
SELECT
    TO_DATE('08/08/2011','dd/mm/yyyy'),
    CASE
        WHEN mod(rownum,2)=0 THEN
            'T'
        ELSE
            'S'
    END,
    'Blah'
FROM
    dual
CONNECT BY
    LEVEL <= 10
insert
into
    LOGTAB
SELECT
    TO_DATE('09/08/2011','dd/mm/yyyy'),
    CASE
        WHEN mod(rownum,2)=0 THEN
            'T'
        ELSE
            'S'
    END,
    'Blah'
FROM
    dual
CONNECT BY
    LEVEL <= 10
insert
into
    LOGTAB
SELECT
    TO_DATE('10/08/2011','dd/mm/yyyy'),
    CASE
        WHEN mod(rownum,2)=0 THEN
            'T'
        ELSE
            'S'
    END,
    'Blah'
FROM
    dual
CONNECT BY
    LEVEL <= 10
insert
into
    LOGTAB
SELECT
    TO_DATE('11/08/2011','dd/mm/yyyy'),
    CASE
        WHEN mod(rownum,2)=0 THEN
            'T'
        ELSE
            'S'
    END,
    'Blah'
FROM
    dual
CONNECT BY
    LEVEL <= 10
SQL> select * from logtab where cdat=to_date('08/08/2011','dd/mm/yyyy');
CDAT      D COL1
08-AUG-11 T Blah
08-AUG-11 T Blah
08-AUG-11 T Blah
08-AUG-11 T Blah
08-AUG-11 T Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
SQL> select table_name,partition_name,subpartition_name from user_tab_subpartitions;
TABLE_NAME                     PARTITION_NAME                 SUBPARTITION_NAME
LOGTAB                         PTN_20110808                   PTN_20110808_SPTN_DEFAULT
LOGTAB                         PTN_20110808                   PTN_20110808_SPTN_T
LOGTAB                         PTN_20110809                   PTN_20110809_SPTN_DEFAULT
LOGTAB                         PTN_20110809                   PTN_20110809_SPTN_T
LOGTAB                         PTN_20110810                   PTN_20110810_SPTN_DEFAULT
LOGTAB                         PTN_20110810                   PTN_20110810_SPTN_T
LOGTAB                         PTN_20110811                   PTN_20110811_SPTN_DEFAULT
LOGTAB                         PTN_20110811                   PTN_20110811_SPTN_T
LOGTAB                         PTN_MAXVALUE                   PTN_MAXVALUE_SPTN_DEFAULT
LOGTAB                         PTN_MAXVALUE                   PTN_MAXVALUE_SPTN_T
10 rows selected.
SQL> alter table logtab truncate subpartition PTN_20110808_SPTN_T;
Table truncated.
Elapsed: 00:00:00.03
SQL> select * from logtab where cdat=to_date('08/08/2011','dd/mm/yyyy');
CDAT      D COL1
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
08-AUG-11 S Blah
Elapsed: 00:00:00.00Not sure if it's suitable for you or not but it could be an option...
HTH
David