2022-06-16 17:48:10 +02:00
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Firebird engine parallel features in v5.
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Author: Vladyslav Khorsun <hvlad at users sourceforge net>
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The Firebird engine can now execute some tasks using multiple threads in
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parallel. Currently parallel execution is implemented for the sweep and the
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index creation tasks. Parallel execution is supported for both auto- and manual
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sweep.
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To handle same task by multiple threads engine runs additional worker threads
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and creates internal worker attachments. By default, parallel execution is not
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enabled. There are two ways to enable parallelism in user attachment:
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- set number of parallel workers in DPB using new tag isc_dpb_parallel_workers,
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- set default number of parallel workers using new setting ParallelWorkers in
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firebird.conf.
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For gfix utility there is new command-line switch -parallel that allows to
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2023-04-16 17:26:02 +02:00
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set number of parallel workers for the "sweep" and "icu" tasks. For example:
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2022-06-16 17:48:10 +02:00
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gfix -sweep -parallel 4 <database>
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will run sweep on given database and ask engine to use 4 workers. gfix uses DPB
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tag isc_dpb_parallel_workers when attaches to <database>, if switch -parallel
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is present.
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New firebird.conf setting ParallelWorkers set default number of parallel
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workers that can be used by any user attachment running parallelizable task.
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Default value is 1 and means no use of additional parallel workers. Value in
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DPB have higher priority than setting in firebird.conf.
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To control number of additional workers that can be created by the engine
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there are two new settings in firebird.conf:
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- ParallelWorkers - set default number of parallel workers that used by user
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attachments.
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Could be overriden by attachment using tag isc_dpb_parallel_workers in DPB.
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- MaxParallelWorkers - limit number of simultaneously used workers for the
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given database and Firebird process.
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Internal worker attachments are created and managed by the engine itself.
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Engine maintains per-database pools of worker attachments. Number of items in
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each of such pool is limited by value of MaxParallelWorkers setting. The pools
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are created by each Firebird process independently.
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In Super Server architecture worker attachments are implemented as light-
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weight system attachments, while in Classic and Super Classic its looks like
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usual user attachments. All worker attachments are embedded into creating
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server process. Thus in Classic architectures there is no additional server
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processes. Worker attachments are present in monitoring tables. Idle worker
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attachment is destroyed after 60 seconds of inactivity. Also, in Classic
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architectures worker attachments are destroyed immediately after last user
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connection detached from database.
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Examples:
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Set in firebird.conf ParallelWorkers = 4, MaxParallelWorkers = 8 and restart
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Firebird server.
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a) Connect to test database not using isc_dpb_parallel_workers in DPB and
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execute "CREATE INDEX ..." SQL statement. On commit the index will be actually
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created and engine will use 3 additional worker attachments. In total, 4
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attachments in 4 threads will work on index creation.
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b) Ensure auto-sweep is enabled for test database. When auto-sweep will run on
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that database, it also will use 3 additional workers (and run within 4 threads).
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c) more than one single task at time could be parallelized: make 2 attachments
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and execute "CREATE INDEX ..." in each of them (of course indices to be built
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should be different). Each index will be created using 4 attachments (1 user
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and 3 worker) and 4 threads.
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d) run gfix -sweep <database> - not specifying switch -parallel: sweep will run
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using 4 attachments in 4 threads.
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d) run gfix -sweep -parallel 2 <database>: sweep will run using 2 attachments in
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2 threads. This shows that value in DPB tag isc_dpb_parallel_workers overrides
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value of setting ParallelWorkers.
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