refactor database engine/options; add column descriptors

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

src/database/map/options.rs

@@ -0,0 +1,26 @@
+use rocksdb::{ReadOptions, ReadTier, WriteOptions};
+
+#[inline]
+pub(crate) fn iter_options_default() -> ReadOptions {
+	let mut read_options = read_options_default();
+	read_options.set_background_purge_on_iterator_cleanup(true);
+	//read_options.set_pin_data(true);
+	read_options
+}
+
+#[inline]
+pub(crate) fn cache_read_options_default() -> ReadOptions {
+	let mut read_options = read_options_default();
+	read_options.set_read_tier(ReadTier::BlockCache);
+	read_options
+}
+
+#[inline]
+pub(crate) fn read_options_default() -> ReadOptions {
+	let mut read_options = ReadOptions::default();
+	read_options.set_total_order_seek(true);
+	read_options
+}
+
+#[inline]
+pub(crate) fn write_options_default() -> WriteOptions { WriteOptions::default() }