more caveats

CAVEATS.md

@@ -14,5 +14,7 @@ Container technology was originally designed for stateless applications. Based o
 
 In its default configuration, Litestack allows one writer at a time to write to the database file, while simultaneously allowing any number of readers to access the database. Generally SQLite is pretty fast in writes, but you should be aware that a long running write operation will prevent any other writers from proceeding, for example creating an index on a very large table will stop other writers until the index creation is finished. There is no concurrent index creation facility in SQLite, yet.
 
+## Litestack does not release the GVL
 
+This also applies to the Ruby SQLite3 gem, when it is performing a query, it will not allow any other threads in the Ruby process to resume until it returns. Care should be taken when writing low latency multi-threaded applications with Litestack, it is generally recommended to use fibers over threads in that case, since everything is serialized anyway it makes sense to avoid the ovreheads of mult-threaded environments