Health Monitor 健康檢查

Types of Health Checks

Health monitor runs the following checks:

• DB Structure Integrity Check—This check verifies the integrity of database files and reports failures if these files are inaccessible, corrupt or inconsistent. If the database is in mount or open mode, this check examines the log files and datafiles listed in the control file. If the database is inNOMOUNT mode, only the control file is checked.

• Data Block Integrity Check—This check detects disk image block corruptions such as checksum failures, head/tail mismatch, and logical inconsistencies within the block. Most corruptions can be repaired using Block Media Recovery. Corrupted block information is also captured in theV$DATABASE_BLOCK_CORRUPTION view. This check does not detect inter-block or inter-segment corruption.

• Redo Integrity Check—This check scans the contents of the redo log for accessibility and corruption, as well as the archive logs, if available. The Redo Integrity Check reports failures such as archive log or redo corruption.

• Undo Segment Integrity Check—This check finds logical undo corruptions. After locating an undo corruption, this check uses PMON and SMON to try to recover the corrupted transaction. If this recovery fails, then Health Monitor stores information about the corruption in V$CORRUPT_XID_LIST. Most undo corruptions can be resolved by forcing a commit.

• Transaction Integrity Check—This check is identical to the Undo Segment Integrity Check except that it checks only one specific transaction.

• Dictionary Integrity Check—This check examines the integrity of core dictionary objects, such as tab$ and col$. It performs the following operations:

  • Verifies the contents of dictionary entries for each dictionary object.

  • Performs a cross-row level check, which verifies that logical constraints on rows in the dictionary are enforced.

  • Performs an object relationship check, which verifies that parent-child relationships between dictionary objects are enforced.

  The Dictionary Integrity Check operates on the following dictionary objects:

  tab$, clu$, fet$, uet$, seg$, undo$, ts$, file$, obj$, ind$, icol$, col$, user$, con$, cdef$, ccol$, bootstrap$, objauth$, ugroup$, tsq$, syn$, view$,typed_view$, superobj$, seq$, lob$, coltype$, subcoltype$, ntab$, refcon$, opqtype$, dependency$, access$, viewcon$, icoldep$, dual$, sysauth$, objpriv$,defrole$, and ecol$.

Running Health Checks Using the DBMS_HM PL/SQL Package

The DBMS_HM procedure for running a health check is called RUN_CHECK. To call RUN_CHECK, supply the name of the check and a name for the run, as follows:

BEGIN
  DBMS_HM.RUN_CHECK('Dictionary Integrity Check', 'my_run');
END;
/

To obtain a list of health check names, run the following query:

SELECT name FROM v$hm_check WHERE internal_check='N';

NAME
----------------------------------------------------------------
DB Structure Integrity Check
Data Block Integrity Check
Redo Integrity Check
Transaction Integrity Check
Undo Segment Integrity Check
Dictionary Integrity Check

Most health checks accept input parameters. You can view parameter names and descriptions with the V$HM_CHECK_PARAM view. Some parameters are mandatory while others are optional. If optional parameters are omitted, defaults are used. The following query displays parameter information for all health checks:

SELECT c.name check_name, p.name parameter_name, p.type,
p.default_value, p.description
FROM v$hm_check_param p, v$hm_check c
WHERE p.check_id = c.id and c.internal_check = 'N'
ORDER BY c.name;

Input parameters are passed in the input_params argument as name/value pairs separated by semicolons (;). The following example illustrates how to pass the transaction ID as a parameter to the Transaction Integrity Check:

BEGIN
  DBMS_HM.RUN_CHECK (
   check_name   => 'Transaction Integrity Check',
   run_name     => 'my_run',
   input_params => 'TXN_ID=7.33.2');
END;
/