The oncheck utility places a shared lock on a table during the following operations, so no other users can perform updates, inserts, or deletes until the check has completed:
If the table does not use page locking, the database server does not place a shared lock on the table when you check an index with the oncheck -ci, -cI, -pk, -pK, -pl, or -pL options. When no shared lock is on the table during an index check, other users can update rows during the check.
By not placing a shared lock on tables using row locks during index checks, the oncheck utility cannot be as accurate in the index check. For absolute assurance of a complete index check, you can execute oncheck with the -x option. With the -x option, oncheck places a shared lock on the table, and no other users can perform updates, inserts, or deletes until the check has completed.
For more information about the -x option, refer to Turn On Locking with -x. For information on shared locks and intent shared locks, see the IBM Informix Performance Guide.
The oncheck utility places a shared lock on system catalog tables when they are checked. It places an exclusive lock on a table when it executes repair options.
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