Db exclusive mode (paradigmxyz#6755)

Co-authored-by: Alexey Shekhirin <[email protected]>

crates/storage/db/src/implementation/mdbx/mod.rs

@@ -63,6 +63,27 @@ pub struct DatabaseArguments {
     log_level: Option<LogLevel>,
     /// Maximum duration of a read transaction. If [None], the default value is used.
     max_read_transaction_duration: Option<MaxReadTransactionDuration>,
+    /// Open environment in exclusive/monopolistic mode. If [None], the default value is used.
+    ///
+    /// This can be used as a replacement for `MDB_NOLOCK`, which don't supported by MDBX. In this
+    /// way, you can get the minimal overhead, but with the correct multi-process and multi-thread
+    /// locking.
+    ///
+    /// If `true` = open environment in exclusive/monopolistic mode or return `MDBX_BUSY` if
+    /// environment already used by other process. The main feature of the exclusive mode is the
+    /// ability to open the environment placed on a network share.
+    ///
+    /// If `false` = open environment in cooperative mode, i.e. for multi-process
+    /// access/interaction/cooperation. The main requirements of the cooperative mode are:
+    /// - Data files MUST be placed in the LOCAL file system, but NOT on a network share.
+    /// - Environment MUST be opened only by LOCAL processes, but NOT over a network.
+    /// - OS kernel (i.e. file system and memory mapping implementation) and all processes that
+    ///   open the given environment MUST be running in the physically single RAM with
+    ///   cache-coherency. The only exception for cache-consistency requirement is Linux on MIPS
+    ///   architecture, but this case has not been tested for a long time).
+    ///
+    /// This flag affects only at environment opening but can't be changed after.
+    exclusive: Option<bool>,
 }
 
 impl DatabaseArguments {
@@ -80,6 +101,12 @@ impl DatabaseArguments {
         self.max_read_transaction_duration = max_read_transaction_duration;
         self
     }
+
+    /// Set the mdbx exclusive flag.
+    pub fn exclusive(mut self, exclusive: Option<bool>) -> Self {
+        self.exclusive = exclusive;
+        self
+    }
 }
 
 /// Wrapper for the libmdbx environment: [Environment]
@@ -247,6 +274,7 @@ impl DatabaseEnv {
             // worsens it for random access (which is our access pattern outside of sync)
             no_rdahead: true,
             coalesce: true,
+            exclusive: args.exclusive.unwrap_or_default(),
             ..Default::default()
         });
         // Configure more readers