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CR-SQLite
Custom Syntax

Custom Syntax

A current eye-sore of CR-SQLite is the use of SELECT statements to invoke functions which do some sort of modification of the database schema. E.g., converting a table to a crdt requires running: SELECT crsql_as_crr('table_name').

Another eye-sore is the requirement to wrap alterations of crrs with crsql_begin_alter and crsql_commit_alter.

Luckily, we're partnering with the folks over at the libsql (opens in a new tab) project to add a dedicated syntax for CRR creation and modification.

Note: we're also converting crsql_as_crr to a virtual table to simplify syntax: https://github.com/vlcn-io/cr-sqlite/issues/181 (opens in a new tab)

CREATE TABLE post (
 id INTEGER PRIMARY KEY NOT NULL,
 views COUNTER,
 content PERITEXT,
 owner_id LWW INTEGER
) AS CausalLengthSet;

The above defines a CRR where:

Ongoing Syntax Proposal

Table Syntax

Each table can be modeled as some sort of set CRDT. Grow only set, observe remove set, causal length set, etc.

Given that, we could add a modified CREATE TABLE that is CREATE [set_type]

Example:

CREATE [SetType] foo ( ... );

Other alternatives would be to keep CREATE TABLE and append some modifier to the end:

CREATE TABLE foo ( ... ) AS [SetType]; -- option 1
CREATE TABLE foo ( ... ) CRDT = [SetType]; -- option 2

Where SetType = CausalLengthSet | GrowOnlySet | DeleteWinsSet | AddWinsSet

Note that, in practice, we may end up only supporting CausalLengthSet given that type can be used to model all of the other sets in user space.

Column Syntax

Within a row, each column can be a specific type of CRDT. The type of CRDT chosen controls the semantics of how that given cell is merged.

Some options for a column:

  1. Last Write Wins Register
  2. Counter
  3. Distributed Fractional Index*
  4. Multi-Value Register
  5. RGA
  6. Peritext

One idea is to add an extra type (the crdt type) to the column type.

Example:

CREATE TABLE foo (
  id PRIMARY KEY NOT NULL,
  views COUNTER,
  content PERITEXT,
  owner_id LWW INTEGER
) AS CausalLengthSet;

Or generally:

CREATE TABLE [table_name] (
  [col_name] [CRDTType] [Type],
  ...
) AS [SetType];

where CRDTType = LWW | Counter | DistFractIndex | MVRegister | RGA | Peritext

* Distributed Fractional Index would need to be parameterized. I can go into more detail on this one after we talk through what has been proposed so far.

https://github.com/libsql/libsql/issues/147#issuecomment-1495970616 (opens in a new tab)

ConstraintsCRR