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54 lines
2.6 KiB
Markdown
54 lines
2.6 KiB
Markdown
## IRCd Database
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IRCd's database is presented here primarily as a persistent Object store.
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In other words, the structure presented by the database can be represented
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with JSON. This is built from the primitives of `column`, `row` and `cell`.
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#### Columns
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While a simple key-value store could naively store a JSON document as a textual
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value, we provide additional structure schematized before opening a database:
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Every member of a JSON object is a `column` in this database. To address members
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within nested objects, we specify a `column` with a "foo.bar.baz" path syntax. This
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puts all columns at the same level in our code, even though they may represent
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deeply nested values.
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#### Rows
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Since `columns` are technically independent key-value stores (they have their own
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index), when an index key is the same between columns we call this a `row`. For basic
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object storage the schema is such that we use the same keys between all columns. For
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example, an index would be a username in a user database. The user database itself
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takes the form of a single JSON object and any member lookup happens on a user's row.
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#### Cells
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A `cell` is a single value in a `column` indexed by a key that should be able to form
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a `row` between columns. Consider the following near-json expression:
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users["root"] = {"password", "foobar"};
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In the users database, we find the `column` "password" and the `row` for "root" and
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set that `cell` to "foobar"
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Consider these expressions for objects at some depth:
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users["root"] = {"password.plaintext", "foobar"};
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users["root"] = {"password", {"plaintext, "foobar"}};
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The column is always found as "password.plaintext". We find it (and can iterate its members
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if it were an object) by string-manipulating these full paths which all sit in a single map
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and are always open, even if the cell is empty for some row.
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### Important notes
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!!!
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The database system is plugged into the userspace context system to facilitate IO. This means
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that an expensive database call (mostly on the read side) that has to do disk IO will suspend
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your userspace context. Remember that when your userspace context resumes on the other side
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of the call, the state of IRCd and even the database itself may have changed. We have a suite
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of tools to mitigate this.
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!!!
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* While the database schema is modifiable at runtime (we can add and remove columns on
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the fly) the database is very picky about opening the exact same way it last closed.
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This means, for now, we have the full object schema explicitly specified when the DB
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is first opened. All columns exist for the lifetime of the DB, whether or not you have
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a handle to them.
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