The sp_iqcheckdb stored procedure

The IQ Database Consistency Checker (DBCC) performs database verification and repair functions. The sp_iqcheckdb stored procedure, in conjunction with server startup options, is the interface to DBCC. You select the different modes of check and repair by specifying an sp_iqcheckdb command string. sp_iqcheckdb reads every database page and checks the consistency of the database, unless you specify otherwise in the command string.

DBCC has three different modes that perform increasing amounts of consistency checking and a repair mode for repairing inconsistent indexes. Each mode checks all database objects, unless individual tables and indexes are specified in the sp_iqcheckdb command string. If you specify individual table names, all indexes within those tables are also checked.

The following command line shows the basic syntax of sp_iqcheckdb.

sp_iqcheckdb 'mode target [...] [ resources resource-percent ]'

mode: { allocation | check | verify } | repair

target: database | database resetclocks | { table table-name | index index-name […] }

If both mode and target are not specified in the parameter string, IQ returns the error message “At least one mode and target must be specified to DBCC.”

The index-name parameter may contain owner and table qualifiers: [[owner.]table-name.]index-name. If owner is not specified, current user and database owner (dbo) are substituted in that order. If table is not specified, then index-name must be unique.

The table-name parameter may contain an owner qualifier: [owner.]table-name. If owner is not specified, current user and database owner (dbo) are substituted in that order. table-name cannot be a temporary or pre-join table.

sp_iqcheckdb 'check index "dbo.ss tab.i2" resources 75'

* The processing time of sp_iqcheckdb repair mode depends on the number of errors repaired.

The execution time of DBCC varies according to the size of the database for an entire database check, the number of tables or indexes specified, and the size of the machine. Checking only a subset of the database, i.e., only specified tables or indexes, requires less time than checking an entire database. Refer to the table in the previous section for processing times of the sp_iqcheckdb modes.

For the best DBCC performance, you should be as specific as possible in the sp_iqcheckdb command string. Use the 'allocation' or 'check' verification mode when possible and specify the names of tables or indexes, if you know exactly which database objects require checking.

In check mode, sp_iqcheckdb performs an internal consistency check on all IQ indexes and checks that each database block has been allocated correctly. All available database statistics are reported. This mode reads all data pages and can detect all types of allocation problems and most types of index inconsistencies. Check mode should run considerably faster than verify mode for most databases.

When to run in check mode:

• If metadata, null count, or distinct count errors are returned when running a query

Examples of check mode:

In verify mode, sp_iqcheckdb performs an intra-index consistency check, in addition to internal index consistency and allocation checking. All available database statistics are reported. The contents of each non-FP index is verified against its corresponding FP index(es). Verify mode reads all data pages and can detect all types of allocation problems and all types of index inconsistencies.

When to run in verify mode:

• If metadata, null count, or distinct count errors are returned when running a query

Examples of verify mode:

In allocation mode, sp_iqcheckdb checks that each database block is allocated correctly according to the internal physical page mapping structures (blockmaps). Database statistics pertaining to allocation are also reported. This mode executes very quickly. Allocation mode, however, does not check index consistency and cannot detect all types of allocation problems.

When to run in allocation mode:

• After forced recovery, run sp_iqcheckdb with the -iqdroplks server switch to reset the allocation map (must use database as the target)

• To check for duplicate or unowned blocks (use database or specific tables or indexes as the target)

• If you encounter page header errors

Examples of allocation mode:

sp_iqcheckdb 'allocation database'

sp_iqcheckdb 'allocation table t1'

sp_iqcheckdb 'allocation index t1c1hg'

The DBCC option resetclocks is used only with allocation mode. The resetclocks option is used in conjunction with forced recovery to convert a multiplex query server to a write server. resetclocks corrects the values of internal database versioning clocks, in the event that these clocks are behind. Do not use the resetclocks option for any other purpose, unless you contact Sybase IQ Technical Support.

The resetclocks option must be run in single user mode and is only allowed with the DBCC command 'allocation database'. resetclocks does not require the -iqdroplks server startup switch. The syntax of the resetclocks command is:

sp_iqcheckdb 'allocation database resetclocks'

The repair mode of sp_iqcheckdb performs detailed index checking and can repair many types of index inconsistencies. Allocation checks are not performed during repair mode. The DBCC output indicates which indexes, if any, were repaired. You must issue a COMMIT command to commit changes from repair mode to make them permanent. After DBCC repairs an index, you should run sp_iqcheckdb again in check mode before committing any changes. If an index is still inconsistent, drop and recreate the index.

When to run in repair mode:

• If index errors are reported in sp_iqcheckdb check or verify mode

Examples of repair mode:

sp_iqcheckdb 'repair database'

sp_iqcheckdb 'repair table t1'

sp_iqcheckdb 'repair index t1c1hg'

You should back up the database before executing sp_iqcheckdb in an index repair mode.