In a recent customer project, I was suffering to delete millions of rows from a LOG table.<\/p>\n\n\n\n
Removing 3 months of data took more than 30 minutes with the best optimization possible.<\/p>\n\n\n\n
After a while, I remembered that a very nice oracle feature existing since Oracle 12cR1 enables us to archive rows automatically.<\/p>\n\n\n\n
Let’s me explain you how it works:<\/p>\n\n\n\n
I have a big table with 10 millions of rows:<\/p>\n\n\n\n
SQL> create table bigtable\nsegment creation immediate\nnologging\nas\nwith generator as (\n select\n rownum id\n from dual\n connect by\n level <= 10000000\n)\nselect\n rownum id,\n mod(rownum-1,3) val1,\n mod(rownum-1,10) val2,\n lpad('x',100,'x') padding\nfrom\n generator v1\norder by\n dbms_random.value\n 21 ;\n\nTable created.\n\nSQL> exec dbms_stats.gather_table_stats('SYS','BIGTABLE');\n\nPL\/SQL procedure successfully completed.\n\nSQL> desc bigtable\n Name Null? Type\n ----------------------------------------- -------- ----------------------------\n ID NUMBER\n VAL1 NUMBER\n VAL2 NUMBER\n PADDING VARCHAR2(100)\n\nSQL> select count(*) from bigtable;\n\n COUNT(*)\n----------\n 10000000\n\nSQL>\n<\/code><\/pre>\n\n\n\nLet’s see the data dispersion related to VAL2 column:<\/p>\n\n\n\n
SQL> select count(*),val2 from bigtable group by val2;\n\n COUNT(*) VAL2\n---------- ----------\n 1000000 6\n 1000000 1\n 1000000 7\n 1000000 8\n 1000000 2\n 1000000 4\n 1000000 5\n 1000000 9\n 1000000 3\n 1000000 0\n\n10 rows selected.\n\nSQL>\n<\/code><\/pre>\n\n\n\nLet’s deleting rows related to VAL2 value = 8 :<\/p>\n\n\n\n
SQL> set timing on\nSQL> delete from bigtable where val2=8;\nSQL > commit;\n\n1000000 rows deleted.\n\nElapsed: 00:00:02.97\nSQL> explain plan for delete from bigtable where val2=8;\n\nExplained.\n\nElapsed: 00:00:00.00\nSQL> select * from table(dbms_xplan.display);\n\nPLAN_TABLE_OUTPUT\n--------------------------------------------------------------------------------\nPlan hash value: 1385633249\n\n-------------------------------------------------------------------------------\n| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |\n-------------------------------------------------------------------------------\n| 0 | DELETE STATEMENT | | 1000K| 2929K| 44506 (1)| 00:00:02 |\n| 1 | DELETE | BIGTABLE | | | | |\n|* 2 | TABLE ACCESS FULL| BIGTABLE | 1000K| 2929K| 44506 (1)| 00:00:02 |\n-------------------------------------------------------------------------------\n\nPredicate Information (identified by operation id):\n\nPLAN_TABLE_OUTPUT\n--------------------------------------------------------------------------------\n---------------------------------------------------\n\n 2 - filter(\"VAL2\"=8)\n\n14 rows selected.\n\nElapsed: 00:00:00.02\nSQL>\n<\/code><\/pre>\n\n\n\nThe rows have been removed and the oracle optimizer does a Full Scan to access the data because there is no Index on the VAL2 column. The DELETE sql statement took about 3 sec to execute.<\/p>\n\n\n\n
For any reason If you want to restore this “deleting” rows, only “flashback” or “restore” from a backup will help you.<\/p>\n\n\n\n
Now let’s enabling ROW ARCHIVAL on the table BIGTABLE:<\/p>\n\n\n\n
SQL> alter table bigtable row archival;\n\nTable altered.\n\nElapsed: 00:00:00.05\nSQL>\n<\/code><\/pre>\n\n\n\nA new hidden column called ora_archive_state<\/em> is created indicating whether a row is archived or not. The column is displayed only via the SELECT command, not in the DESC command.<\/p>\n\n\n\nSQL> desc bigtable\n Name Null? Type\n ----------------------------------------- -------- ----------------------------\n ID NUMBER\n VAL1 NUMBER\n VAL2 NUMBER\n PADDING VARCHAR2(100)\n\nSQL> select ID,VAL1,VAL2,PADDING,ora_archive_state from bigtable where rownum = 1;\n\nID VAL1 VAL2 PADDING ORA_ARCHIVE_STATE\n--------------------------------------------------------------------------------\n4091832 2 1 xxxxxxxxxxx 0\n\n\nElapsed: 00:00:00.00\nSQL>\n<\/code><\/pre>\n\n\n\n The value 0 in the ora_archive_state <\/em>means the row is not archived, thus visible via the SELECT.<\/p>\n\n\n\nLet’s confirm all rows are active (not archived):<\/p>\n\n\n\n
SQL> select count(*) from bigtable;\n\n COUNT(*)\n----------\n 10000000\n<\/code><\/pre>\n\n\n\nNow let’s suppose we want to archive all rows having value VAL2=6.<\/p>\n\n\n\n
Lets’s modify the value of ora_archive_state<\/em>:<\/p>\n\n\n\n<\/p>\n\n\n\n
SQL> update bigtable set ora_archive_state=dbms_ilm.archivestatename(1) where val2=6;\n\n1000000 rows updated.\n\nElapsed: 00:00:37.94\nSQL> commit;\n\nCommit complete.\n\nElapsed: 00:00:01.28\nSQL>\n<\/code><\/pre>\n\n\n\nLet’s count the number of rows active now:<\/p>\n\n\n\n
SQL> select count(*) from bigtable;\n\n COUNT(*)\n----------\n 8000000\n\nElapsed: 00:00:02.17\nSQL>\n<\/code><\/pre>\n\n\n\nThe rows archived are no more visible, they have been deleted “logically” (or archived):<\/p>\n\n\n\n
If we want to view all rows archived or not, set the archival visibility to ALL for the session:<\/p>\n\n\n\n
SQL> alter session set row archival visibility = all;\n\nSession altered.\n\nElapsed: 00:00:00.00\n\nSQL> select count(*) from bigtable;\n\n COUNT(*)\n----------\n 90000000\n\nSQL> select count(*),val2,ora_archive_state from bigtable group by val2, ora_archive_state;\n\n COUNT(*) VAL2 ORA_ARCHIVE_STATE\n--------------------------------------------------------------------------------\n1000000 1 0\n1000000 4 0\n1000000 6 1\n1000000 3 0\n1000000 5 0\n1000000 9 0\n1000000 7 0\n1000000 2 0\n1000000 0 0\n\n9 rows selected.\n<\/code><\/pre>\n\n\n\nTo see only rows unarchived, set the archival visibility to ACTIVE:<\/p>\n\n\n\n
SQL> alter session set row archival visibility = active;\n\nSession altered.\n\nElapsed: 00:00:00.00\nSQL> select count(*),val2,ora_archive_state from bigtable group by val2, ora_archive_state;\n\n COUNT(*) VAL2 O\n---------- ---------- -\n 1000000 1 0\n 1000000 7 0\n 1000000 2 0\n 1000000 4 0\n 1000000 5 0\n 1000000 9 0\n 1000000 3 0\n 1000000 0 0\n\n8 rows selected.\n\n<\/code><\/pre>\n\n\n\nCONCLUSION<\/h2>\n\n\n\n
Oracle Database Row Archiving enables you to archive and delete “logically” the rows.<\/p>\n\n\n\n
Generally, it can be used to archive rows in big table.<\/p>\n\n\n\n
The implementation of this feature is very easy and can help you when you have to deal archiving\/deleting rows in big table.<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
In a recent customer project, I was suffering to delete millions of rows from a LOG table. Removing 3 months of data took more than 30 minutes with the best optimization possible. After a while, I remembered that a very nice oracle feature existing since Oracle 12cR1 enables us to archive rows automatically. Let’s me […]<\/p>\n","protected":false},"author":27,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229,198,368],"tags":[1171,2203],"type_dbi":[],"class_list":["post-19870","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","category-database-management","category-development-performance","tag-oracle-19c","tag-oracle-database"],"acf":[],"yoast_head":"\n
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