refactor database engine/options; add column descriptors

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

src/database/engine/memory_usage.rs

@@ -0,0 +1,30 @@
+use std::fmt::Write;
+
+use conduwuit::{implement, Result};
+use rocksdb::perf::get_memory_usage_stats;
+
+use super::Engine;
+use crate::or_else;
+
+#[implement(Engine)]
+pub fn memory_usage(&self) -> Result<String> {
+	let mut res = String::new();
+	let stats = get_memory_usage_stats(Some(&[&self.db]), Some(&[&*self.ctx.row_cache.lock()?]))
+		.or_else(or_else)?;
+	let mibs = |input| f64::from(u32::try_from(input / 1024).unwrap_or(0)) / 1024.0;
+	writeln!(
+		res,
+		"Memory buffers: {:.2} MiB\nPending write: {:.2} MiB\nTable readers: {:.2} MiB\nRow \
+		 cache: {:.2} MiB",
+		mibs(stats.mem_table_total),
+		mibs(stats.mem_table_unflushed),
+		mibs(stats.mem_table_readers_total),
+		mibs(u64::try_from(self.ctx.row_cache.lock()?.get_usage())?),
+	)?;
+
+	for (name, cache) in &*self.ctx.col_cache.lock()? {
+		writeln!(res, "{name} cache: {:.2} MiB", mibs(u64::try_from(cache.get_usage())?))?;
+	}
+
+	Ok(res)
+}