mirror of
https://github.com/matrix-construct/construct
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57 lines
2.6 KiB
Markdown
57 lines
2.6 KiB
Markdown
# Database Schema
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This system provides local storage for all events and related metadata using
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the `events` database. The database is divided into several columns.
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Writing to the database must only occur through the single `write()` call,
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which operates using transactions. In fact, `write()` itself only builds
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transactions and does not actually modify the database until the user commits
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the transaction.
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Reading from the database can occur more directly by referencing the columns
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and using the `ircd::db` API's.
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```
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Note for casual developers: This is low-level API. It is highly likely what
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you are looking for has a real interface somewhere in ircd::m.
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```
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### Column Overview
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There are two categories of columns: Direct event data, and indirect metadata.
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The only data stored by the server is in the form of matrix events in rooms.
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No arbitrary application data is stored in the database. For example, there
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is no "accounts column" storing some user account information; instead this
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would be implemented as some matrix event with the type like `ircd.account`
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and the `content` containing our arbitrary data.
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The only metadata stored in addition to the original event data optimizes and
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enhances the original event data. Again, no arbitrary application data is
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stored here. Everything stored here helps to facilitate the service of events
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inside rooms, for any reasonable purpose, which we then build the application
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layer on top of.
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#### Direct columns
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Direct data consists of original event JSON in addition to several direct
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property columns. The fundamental event JSON is stored in `_event_json`.
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Select properties from the original JSON are also stored in tuned columns
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(see: event_column.h).
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The event_column(s) all store duplicate data from the original _event_json
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but limited to a single specific property. The index key is an event_idx
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(just like _event_json). These columns are useful for various optimizations
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at the cost of the additional space consumed.
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When conducting a point lookup of an event property with m::get() or with
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keys masked in m::event::fetch::opts, these columns handle the query iff
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all desired properties can be satisfied from these columns; otherwise
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if a property is sought which does not have an active corresponding column
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here the _event_json is used transparently to satisfy the query.
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Cache and storage details here can be tuned specific to each property. This
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makes reading faster and cache footprints more compact, holding much larger
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datasets without eviction; in addition to not disrupting the widely shared
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_event_json cache during a simple iteration of one property for all events
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on the server, etc.
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