database: add redb-memory backend (#97)

* add `redb-memory` feature

* redb: use `redb::backend::InMemoryBackend` if enabled

* readme: add `redb-memory` section

* ci: add `redb-memory` testing

* ci: remove `redb-memory` testing

probably not worth adding time to CI for this

database/Cargo.toml

@@ -9,10 +9,12 @@ repository  = "https://github.com/Cuprate/cuprate/tree/main/database"
 keywords    = ["cuprate", "database"]
 
 [features]
-default   = ["heed", "redb", "service"]
+# default   = ["heed", "redb", "service"]
 # default   = ["redb", "service"]
+default   = ["redb-memory", "service"]
 heed       = ["dep:heed"]
 redb       = ["dep:redb"]
+redb-memory = ["redb"]
 service     = ["dep:crossbeam", "dep:futures", "dep:tokio", "dep:tokio-util", "dep:tower", "dep:rayon"]
 
 [dependencies]

database/README.md

@@ -11,6 +11,7 @@ Cuprate's database implementation.
 1. [Backends](#backends)
     - [`heed`](#heed)
     - [`redb`](#redb)
+    - [`redb-memory`](#redb-memory)
     - [`sanakirja`](#sanakirja)
     - [`MDBX`](#mdbx)
 1. [Layers](#layers)
@@ -165,6 +166,11 @@ The upstream versions from [`crates.io`](https://crates.io/crates/redb) are used
 
 TODO: document DB on remote filesystem (does redb allow this?)
 
+## `redb-memory`
+This backend is 100% the same as `redb`, although, it uses `redb::backend::InMemoryBackend` which is a key-value store that completely resides in memory instead of a file.
+
+All other details about this should be the same as the normal `redb` backend.
+
 ## `sanakirja`
 [`sanakirja`](https://docs.rs/sanakirja) was a candidate as a backend, however there were problems with maximum value sizes.
 

database/src/backend/redb/env.rs

@@ -72,6 +72,10 @@ impl Env for ConcreteEnv {
         // TODO: we can set cache sizes with:
         // env_builder.set_cache(bytes);
 
+        // Use the in-memory backend if the feature is enabled.
+        let mut env = if cfg!(feature = "redb-memory") {
+            env_builder.create_with_backend(redb::backends::InMemoryBackend::new())?
+        } else {
             // Create the database directory if it doesn't exist.
             std::fs::create_dir_all(config.db_directory())?;
 
@@ -81,7 +85,9 @@ impl Env for ConcreteEnv {
                 .write(true)
                 .create(true)
                 .open(config.db_file())?;
-        let mut env = env_builder.create_file(db_file)?;
+
+            env_builder.create_file(db_file)?
+        };
 
         // Create all database tables.
         // `redb` creates tables if they don't exist.