mirror of
https://github.com/matrix-construct/construct
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112 lines
4.3 KiB
C++
112 lines
4.3 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_M_EVENT_FETCH_H
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/// Event Fetcher (local).
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///
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/// Fetches event data from the local database and populates an m::event which
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/// is a parent of this class; an instance of this object can be used as an
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/// `m::event` via that upcast. The data backing this `m::event` is a zero-copy
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/// reference into the database and its lifetime is governed by the internals
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/// of this object.
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///
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/// This can be constructed from either an event::idx or an `event_id`; the
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/// latter will incur an extra m::index() lookup. The constructor will throw
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/// for a missing event; the nothrow overloads will set a boolean indicator
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/// instead. A default constructor can also be used; after construction the
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/// seek() ADL suite can be used to the above effect.
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///
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/// The data is populated by one of two query types to the database; this is
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/// determined automatically by default, but can be configured further with
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/// the options structure.
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///
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struct ircd::m::event::fetch
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:event
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{
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struct opts;
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using keys = event::keys;
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using view_closure = std::function<void (const string_view &)>;
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static const opts default_opts;
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const opts *fopts {&default_opts};
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idx event_idx {0};
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std::array<db::cell, event::size()> cell;
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db::cell _json;
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db::row row;
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bool valid;
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id::buf event_id_buf;
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static string_view key(const event::idx *const &);
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static bool should_seek_json(const opts &);
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bool assign_from_row(const string_view &key);
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bool assign_from_json(const string_view &key);
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public:
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explicit fetch(const idx &, const id &, std::nothrow_t, const opts & = default_opts);
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fetch(const idx &, std::nothrow_t, const opts & = default_opts);
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fetch(const id &, std::nothrow_t, const opts & = default_opts);
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fetch(const id &, const opts & = default_opts);
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fetch(const idx &, const opts & = default_opts);
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fetch(const opts & = default_opts);
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};
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namespace ircd::m
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{
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bool seek(event::fetch &, const event::idx &, const event::id &, std::nothrow_t);
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bool seek(event::fetch &, const event::idx &, std::nothrow_t);
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void seek(event::fetch &, const event::idx &);
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bool seek(event::fetch &, const event::id &, std::nothrow_t);
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void seek(event::fetch &, const event::id &);
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}
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/// Event Fetch Options.
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///
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/// Refer to the individual member documentations for details. Notes:
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///
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/// - The default keys selection is *all keys*. This is unnecessarily
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/// expensive I/O for most uses of event::fetch; consider narrowing the keys
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/// selection based on what properties of the `m::event` will be accessed.
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///
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/// - Row Query: The event is populated by conducting a set of point lookups
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/// for the selected keys. The point lookups are parallelized so the latency
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/// of a lookup is only limited to the slowest key. The benefit of this type
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/// is that very efficient I/O and caching can be conducted, but the cost is
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/// that each lookup in the row occupies a hardware I/O lane which is a limited
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/// resource shared by the whole system.
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///
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/// - JSON Query: The event is populated by conducting a single point lookup
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/// to a database value containing the full JSON string of the event. This
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/// query is made when all keys are selected. The benefit of this query is that
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/// it only occupies one hardware I/O lane in contrast with the row query. The
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/// cost is that the full event JSON is read from storage (up to 64_KiB) and
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/// maintained in cache.
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///
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struct ircd::m::event::fetch::opts
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{
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/// Event property selector
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event::keys::selection keys;
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/// Database get options passthru
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db::gopts gopts;
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/// Whether to force an attempt at populating the event from event_json
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/// first, bypassing any decision-making. This is useful if a key selection
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/// is used which would trigger a row query but the developer wants the
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/// json query anyway.
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bool query_json_force {false};
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opts(const event::keys::selection &, const db::gopts & = {});
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opts(const db::gopts &, const event::keys::selection & = {});
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opts() = default;
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};
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