An Index Often Becomes Unusable

Question

Hi,
An index becomes unusable...almost on a daily basis..sometimes it 'fixes' itself and goes back to normal...
What would (usually) cause that? How can I mitigate this?
CREATE INDEX myschema.IDX_DATE_TG_DMA_STATE ON myschema.S_A_LOG (TG ASC, STATE ASC, DMA ASC, A_DATE ASC) NOPARALLEL;

Answer 1

There shouldn't be any structural change. Here's what I got in dba_jobs
DBA_JOBS
3     AVAIL     AVAIL     AVAIL     10-DEC-07 04.00     04:00:03               11-DEC-07 04.00     04:00:00     1678     N     trunc(sysdate+1)+4/24     0     GEN_SEGMENT_SPACE_STATS;     NLS_LANGUAGE='AMERICAN' NLS_TERRITORY='AMERICA' NLS_CURRENCY='$' NLS_ISO_CURRENCY='AMERICA' NLS_NUMERIC_CHARACTERS='.,' NLS_DATE_FORMAT='DD-MON-RR' NLS_DATE_LANGUAGE='AMERICAN' NLS_SORT='BINARY'
2     SYS     SYSMAN     SYSMAN     10-DEC-07 09.30     09:30:54               10-DEC-07 09.31     09:31:54     13711.0000000000000000000000000000000056     N     sysdate + 1 / (24 * 60)     0     EMD_MAINTENANCE.EXECUTE_EM_DBMS_JOB_PROCS();     NLS_LANGUAGE='AMERICAN' NLS_TERRITORY='AMERICA' NLS_CURRENCY='$' NLS_ISO_CURRENCY='AMERICA' NLS_NUMERIC_CHARACTERS='.,' NLS_DATE_FORMAT='DD-MON-RR' NLS_DATE_LANGUAGE='AMERICAN' NLS_SORT='BINARY'
4     AVAIL     AVAIL     AVAIL     10-DEC-07 04.30     04:30:03               11-DEC-07 04.30     04:30:00     641     N     trunc(sysdate+1)+4.5/24     0     GEN_DATAFILE_SPACE_USAGE;     NLS_LANGUAGE='AMERICAN' NLS_TERRITORY='AMERICA' NLS_CURRENCY='$' NLS_ISO_CURRENCY='AMERICA' NLS_NUMERIC_CHARACTERS='.,' NLS_DATE_FORMAT='DD-MON-RR' NLS_DATE_LANGUAGE='AMERICAN' NLS_SORT='BINARY'