mirror of
https://github.com/matrix-construct/construct
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68 lines
2.2 KiB
C++
68 lines
2.2 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_DB_COMPACTOR_H
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namespace ircd::db
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{
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struct compactor;
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}
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/// Compaction callback
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///
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/// return db::op::GET (0) from callback for no-op
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/// return db::op::DELETE from callback to delete this kv.
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/// return db::op::SET from callback if replacement modified.
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/// return db::op::DELETE_RANGE from callback if skip_until modified.
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///
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/// Please note the exact mechanism of the return value from the closure. This
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/// is an operation during a specific compaction, not a front-end operation on
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/// the database.
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///
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/// - op::GET the source record is moved to the target as per normal
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/// compaction.
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///
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/// - op::SET the new value is placed in the compaction target rather than
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/// the source value. Specify the new value at `replace` in the args struct.
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///
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/// - op::DELETE a delete record is placed in the compaction target and the
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/// source value will be forgotten.
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///
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/// - op::DELETE_RANGE skips moving the source record to the target. The
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/// source record is simply forgotten without a delete record. User can set
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/// `skip_until` in the args structure to apply this non-action to a range.
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///
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struct ircd::db::compactor
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{
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struct args;
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using proto = db::op (const args &);
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using callback = std::function<proto>;
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callback value;
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callback merge;
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};
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/// The arguments presented to the callback are aggregated in this structure.
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///
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/// For each record iterated in the compaction we present const information
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/// for examination by the user in the first part of this structure. It also
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/// contains an interface for the compactor to mutate records during the
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/// process.
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///
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struct ircd::db::compactor::args
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{
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const int &level;
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const string_view key;
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const string_view val;
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std::string *const &replace;
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std::string *const &skip_until;
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};
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