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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "i_thread_service.h"
namespace vespalib { class ISequencedTaskExecutor; }
namespace searchcorespi::index {
/**
* Interface for the thread model used for write tasks for a single document database.
*
* We have multiple write threads:
*
* 1. The "master" write thread used for the majority of write tasks.
*
* 2. The "index" write thread used for doing changes to the memory
* index, either directly (for data not bound to a field) or via
* index field inverter executor or index field writer executor.
*
* 3. The "summary" thread is used for doing changes to the document store.
*
* 4. The "index field inverter" executor is used to populate field
* inverters with data from document fields. Scheduled tasks for
* the same field are executed in sequence.
*
* 5. The "index field writer" executor is used to sort data in field
* inverters before pushing the data to the memory field indexes.
* Scheduled tasks for the same field are executed in sequence.
*
* 6. The "attribute field writer" executor is used to write data to attribute vectors.
* Each attribute is always handled by the same thread,
* and scheduled tasks for the same attribute are executed in sequence.
*
* The master write thread is always the one giving tasks to the other write threads above.
*
* In addition this interface exposes the "shared" executor that is used by all document databases.
* This is among others used for compressing / de-compressing documents in the document store,
* merging files as part of disk index fusion, and running the prepare step when doing two-phase
* puts against a tensor attribute with a HNSW index.
*
* The index write thread extracts fields from documents and gives
* task to the index field inverter executor and the index field
* writer executor.
*
* The index field inverter executor and index field writer executor
* are separate to allow for double buffering, i.e. populate one set
* of field inverters using the index field inverter executor while
* another set of field inverters are handled by the index field
* writer executor.
*
* We might decide to allow index field inverter tasks to schedule
* tasks to the index field writer executor, so draining logic needs
* to sync index field inverter executor before syncing index field
* writer executor.
*
* TODO: * indexFieldInverter and indexFieldWriter can be collapsed to one. Both need sequencing,
* but they sequence on different things so efficiency will be the same and just depends on #threads
*/
struct IThreadingService
{
IThreadingService(const IThreadingService &) = delete;
IThreadingService & operator = (const IThreadingService &) = delete;
IThreadingService() = default;
virtual ~IThreadingService() = default;
virtual void sync_all_executors() = 0;
virtual IThreadService &master() = 0;
virtual IThreadService &index() = 0;
virtual IThreadService &summary() = 0;
virtual vespalib::ThreadExecutor &shared() = 0;
virtual vespalib::ISequencedTaskExecutor &indexFieldInverter() = 0;
virtual vespalib::ISequencedTaskExecutor &indexFieldWriter() = 0;
virtual vespalib::ISequencedTaskExecutor &attributeFieldWriter() = 0;
};
}
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