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91 lines
3.9 KiB
Plaintext
91 lines
3.9 KiB
Plaintext
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Database validation allows to run low-level checks of consistency of on-disk
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structures and even to fix some minor corruptions. It is recommended procedure
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for any valuable database, i.e. DBA should validate database from time to time
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to make sure it is healthy. But validation process requires exclusive access to
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database, i.e. it forbids any kind of concurrent access to database while
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validation runs. It could be a big problem to stop user access, especially when
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database is large and validation takes notable amount of time.
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Online validation is a new feature which allows to perform some consistency
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checks without exclusive access to database. Online validation allows to:
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- validate some (or all) user tables in database
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- validate some (or all) indices
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- system tables are not validated
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- other ODS checks (such as Header\PIP\TIP\Generators pages) are not run by
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online validation
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- while table (and/or its index) is validated user attachments are allowed to
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read this table. Attempt to INSERT\UPDATE\DELETE will wait until validation
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finished or will return lock timeout error (depends on lock timeout of user
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transaction)
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- while table (and/or its index) is validated any kind of garbage collection at
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this table is disabled - background and cooperative garbage collection will
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just skip this table, sweep will be terminated with error.
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When online validation starts to check table it makes few actions to prevent
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concurrent modifications of table's data:
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- acquires relation lock in PR (protected read) mode
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- acquires (new) garbage collection lock in PW (protected write) mode.
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Both locks are acquired using user-specified lock timeout. If any lock request
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fails error is reported and table is skipped.
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Then table and its indices are validated in the same way as full validation does.
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Then locks are released and next table is validated.
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Online validation is implemented as Firebird service and accessible via Services
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API. Therefore gfix utility can't run online validation. fbsvcmgr utility has
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full support for new service, syntax is:
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fbsvcmgr [host:]service_mgr [user <...>] [password <...>]
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action_validate dbname <filename>
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[val_tab_incl <pattern>]
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[val_tab_excl <pattern>]
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[val_idx_incl <pattern>]
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[val_idx_excl <pattern>]
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[val_lock_timeout <number>]
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where
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val_tab_incl pattern for tables names to include in validation run
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val_tab_excl pattern for tables names to exclude from validation run
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val_idx_incl pattern for indices names to include in validation run,
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by default %, i.e. all indices
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val_idx_excl pattern for indices names to exclude from validation run
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val_lock_timeout lock timeout, used to acquire locks for table to validate,
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in seconds, default is 10 sec
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0 is no-wait
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-1 is infinite wait
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Patterns are regular expressions, they are processed by the same rules as
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"SIMILAR TO" expressions. All patterns are case-sensitive (despite of database
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dialect!).
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If pattern for tables is omitted then all user tables will be validated.
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If pattern for indices is omitted then all indices of tables to validate will
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be validated.
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System tables are not validated.
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Examples:
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1. fbsvcmgr.exe service_mgr user SYSDBA password masterkey
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action_validate dbname c:\db.fdb
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val_tab_incl A%
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val_idx_excl %
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val_lock_timeout 0
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this command will validate all tables in database "c:\db.fdb" with names
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starting with "A". Indices are not validated. Lock wait is not performed.
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2. fbsvcmgr.exe service_mgr user SYSDBA password masterkey
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action_validate dbname c:\db.fdb
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val_tab_incl "TAB1|TAB2"
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this command will validate tables TAB1 and TAB2 and all their indices.
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Lock wait timeout is 10 sec.
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Note, to specify list of tables/indices it is necessary to:
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a) separate names by character "|"
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b) don't use spaces : TAB1 | TAB2 is wrong
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c) whole list should be enclosed in double quotes to not confuse command
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interpreter
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Vlad Khorsun, <hvlad at users sourceforge net>
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