Add option to bypass dropped column erasure.

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/config/mod.rs

@@ -1273,6 +1273,20 @@ pub struct Config {
 	#[serde(default = "default_rocksdb_stats_level")]
 	pub rocksdb_stats_level: u8,
 
+	/// Erases data no longer reachable in the current schema. The developers
+	/// expect this to be set to true which simplifies the schema and prevents
+	/// accumulation of old schemas remaining in the codebase forever. If this
+	/// is set to false, old columns which are not described in the current
+	/// schema will be ignored rather than erased, leaking their space.
+	///
+	/// This can be set to false when moving between versions in ways which are
+	/// not recommended or otherwise forbidden, or for diagnostic and
+	/// development purposes; requiring preservation across such movements.
+	///
+	/// default: true
+	#[serde(default = "true_fn")]
+	pub rocksdb_drop_missing_columns: bool,
+
 	/// This is a password that can be configured that will let you login to the
 	/// server bot account (currently `@conduit`) for emergency troubleshooting
 	/// purposes such as recovering/recreating your admin room, or inviting

src/database/engine/open.rs

@@ -103,7 +103,10 @@ fn configure_cfds(
 		debug!("Creating new column {name:?} not previously found in existing database.");
 	});
 
-	let missing_descriptors = missing.clone().map(|_| descriptor::DROPPED);
+	let missing_descriptors = missing
+		.clone()
+		.filter(|_| config.rocksdb_drop_missing_columns)
+		.map(|_| descriptor::DROPPED);
 
 	let cfopts: Vec<_> = desc
 		.iter()

src/database/mod.rs

@@ -1,4 +1,4 @@
-#![type_length_limit = "3072"]
+#![type_length_limit = "8192"]
 
 extern crate rust_rocksdb as rocksdb;
 

tuwunel-example.toml

@@ -1080,6 +1080,18 @@
 #
 #rocksdb_stats_level = 1
 
+# Erases data no longer reachable in the current schema. The developers
+# expect this to be set to true which simplifies the schema and prevents
+# accumulation of old schemas remaining in the codebase forever. If this
+# is set to false, old columns which are not described in the current
+# schema will be ignored rather than erased, leaking their space.
+#
+# This can be set to false when moving between versions in ways which are
+# not recommended or otherwise forbidden, or for diagnostic and
+# development purposes; requiring preservation across such movements.
+#
+#rocksdb_drop_missing_columns = true
+
 # This is a password that can be configured that will let you login to the
 # server bot account (currently `@conduit`) for emergency troubleshooting
 # purposes such as recovering/recreating your admin room, or inviting