Allows to have secondary instances in memory

lib/src/storage/backend/rocksdb.rs

@@ -101,8 +101,8 @@ struct RwDbHandler {
     column_family_names: Vec<&'static str>,
     cf_handles: Vec<*mut rocksdb_column_family_handle_t>,
     cf_options: Vec<*mut rocksdb_options_t>,
-    path: PathBuf,
     in_memory: bool,
+    path: PathBuf,
 }
 
 unsafe impl Send for RwDbHandler {}
@@ -130,8 +130,9 @@ impl Drop for RwDbHandler {
             rocksdb_options_destroy(self.options);
             rocksdb_block_based_options_destroy(self.block_based_table_options);
         }
-        if self.in_memory && self.path.exists() {
-            remove_dir_all(&self.path).unwrap();
+        if self.in_memory {
+            #[allow(clippy::let_underscore_must_use)]
+            let _ = remove_dir_all(&self.path);
         }
     }
 }
@@ -144,6 +145,7 @@ struct RoDbHandler {
     cf_handles: Vec<*mut rocksdb_column_family_handle_t>,
     cf_options: Vec<*mut rocksdb_options_t>,
     is_secondary: bool,
+    path_to_remove: Option<PathBuf>,
 }
 
 unsafe impl Send for RoDbHandler {}
@@ -163,34 +165,29 @@ impl Drop for RoDbHandler {
             rocksdb_readoptions_destroy(self.read_options);
             rocksdb_options_destroy(self.options);
         }
+        if let Some(path) = &self.path_to_remove {
+            #[allow(clippy::let_underscore_must_use)]
+            let _ = remove_dir_all(path);
+        }
     }
 }
 
 impl Db {
     pub fn new(column_families: Vec<ColumnFamilyDefinition>) -> Result<Self, StorageError> {
-        let path = if cfg!(target_os = "linux") {
-            "/dev/shm/".into()
-        } else {
-            temp_dir()
-        }
-        .join(format!("oxigraph-rocksdb-{}", random::<u128>()));
-        Self::open_read_write(path, column_families, true)
+        Self::open_read_write(None, column_families)
     }
 
-    pub fn open(
-        path: &Path,
+    pub fn open_read_write(
+        path: Option<&Path>,
         column_families: Vec<ColumnFamilyDefinition>,
     ) -> Result<Self, StorageError> {
-        Self::open_read_write(path.into(), column_families, false)
-    }
-
-    fn open_read_write(
-        path: PathBuf,
-        column_families: Vec<ColumnFamilyDefinition>,
-        in_memory: bool,
-    ) -> Result<Self, StorageError> {
-        unsafe {
+        let (path, in_memory) = if let Some(path) = path {
+            (path.to_path_buf(), false)
+        } else {
+            (tmp_path(), true)
+        };
         let c_path = path_to_cstring(&path)?;
+        unsafe {
             let options = Self::db_options(true, in_memory)?;
             rocksdb_options_set_create_if_missing(options, 1);
             rocksdb_options_set_create_missing_column_families(options, 1);
@@ -320,8 +317,8 @@ impl Db {
                     column_family_names,
                     cf_handles,
                     cf_options,
-                    path,
                     in_memory,
+                    path,
                 })),
             })
         }
@@ -329,12 +326,17 @@ impl Db {
 
     pub fn open_secondary(
         primary_path: &Path,
-        secondary_path: &Path,
+        secondary_path: Option<&Path>,
         column_families: Vec<ColumnFamilyDefinition>,
     ) -> Result<Self, StorageError> {
-        unsafe {
         let c_primary_path = path_to_cstring(primary_path)?;
-            let c_secondary_path = path_to_cstring(secondary_path)?;
+        let (secondary_path, in_memory) = if let Some(path) = secondary_path {
+            (path.to_path_buf(), false)
+        } else {
+            (tmp_path(), true)
+        };
+        let c_secondary_path = path_to_cstring(&secondary_path)?;
+        unsafe {
             let options = Self::db_options(false, false)?;
             let (column_family_names, c_column_family_names, cf_options) =
                 Self::column_families_names_and_options(column_families, options);
@@ -385,6 +387,11 @@ impl Db {
                     cf_handles,
                     cf_options,
                     is_secondary: true,
+                    path_to_remove: if in_memory {
+                        Some(secondary_path)
+                    } else {
+                        None
+                    },
                 })),
             })
         }
@@ -447,6 +454,7 @@ impl Db {
                     cf_handles,
                     cf_options,
                     is_secondary: false,
+                    path_to_remove: None,
                 })),
             })
         }
@@ -1428,3 +1436,12 @@ fn available_file_descriptors() -> io::Result<Option<u64>> {
 fn available_file_descriptors() -> io::Result<Option<u64>> {
     Ok(None)
 }
+
+fn tmp_path() -> PathBuf {
+    if cfg!(target_os = "linux") {
+        "/dev/shm/".into()
+    } else {
+        temp_dir()
+    }
+    .join(format!("oxigraph-rocksdb-{}", random::<u128>()))
+}

lib/src/storage/mod.rs

@@ -87,17 +87,26 @@ impl Storage {
 
     #[cfg(not(target_family = "wasm"))]
     pub fn open(path: &Path) -> Result<Self, StorageError> {
-        Self::setup(Db::open(path, Self::column_families())?)
+        Self::setup(Db::open_read_write(Some(path), Self::column_families())?)
     }
 
     #[cfg(not(target_family = "wasm"))]
-    pub fn open_secondary(
+    pub fn open_secondary(primary_path: &Path) -> Result<Self, StorageError> {
+        Self::setup(Db::open_secondary(
+            primary_path,
+            None,
+            Self::column_families(),
+        )?)
+    }
+
+    #[cfg(not(target_family = "wasm"))]
+    pub fn open_persistent_secondary(
         primary_path: &Path,
         secondary_path: &Path,
     ) -> Result<Self, StorageError> {
         Self::setup(Db::open_secondary(
             primary_path,
-            secondary_path,
+            Some(secondary_path),
             Self::column_families(),
         )?)
     }

lib/src/store.rs

@@ -106,26 +106,48 @@ impl Store {
         })
     }
 
-    /// Opens a read-only clone of a running [`Store`].
+    /// Opens a read-only clone of a running read-write [`Store`].
+    ///
+    /// Changes done while this process is running will be replicated after a possible lag.
+    ///
+    /// It should only be used if a primary instance opened with [`Store::open`] is running at the same time.
+    /// `primary_path` must be the path of the primary instance.
+    /// This secondary instance will use temporary storage for the secondary instance cache.
+    /// If you prefer persistent storage use [`Store::open_persistent_secondary`].
+    ///
+    /// If you want to simple read-only [`Store`] use [`Store::open_read_only`].
+    #[cfg(not(target_family = "wasm"))]
+    pub fn open_secondary(primary_path: impl AsRef<Path>) -> Result<Self, StorageError> {
+        Ok(Self {
+            storage: Storage::open_secondary(primary_path.as_ref())?,
+        })
+    }
+
+    /// Opens a read-only clone of a running read-write [`Store`] with persistence of the secondary instance cache.
+    ///
+    /// Changes done while this process is running will be replicated after a possible lag.
     ///
     /// It should only be used if a primary instance opened with [`Store::open`] is running at the same time.
     /// `primary_path` must be the path of the primary instance and `secondary_path` an other directory for the secondary instance cache.
     ///
     /// If you want to simple read-only [`Store`] use [`Store::open_read_only`].
     #[cfg(not(target_family = "wasm"))]
-    pub fn open_secondary(
+    pub fn open_persistent_secondary(
         primary_path: impl AsRef<Path>,
         secondary_path: impl AsRef<Path>,
     ) -> Result<Self, StorageError> {
         Ok(Self {
-            storage: Storage::open_secondary(primary_path.as_ref(), secondary_path.as_ref())?,
+            storage: Storage::open_persistent_secondary(
+                primary_path.as_ref(),
+                secondary_path.as_ref(),
+            )?,
         })
     }
 
     /// Opens a read-only [`Store`] from disk.
     ///
-    /// It should not be already opened in write mode.
-    /// If you want to do so, use [`Store::open_secondary`].
+    /// Opening as read-only while having an other process writing the database is undefined behavior.
+    /// [`Store::open_secondary`] should be used in this case.
     #[cfg(not(target_family = "wasm"))]
     pub fn open_read_only(path: impl AsRef<Path>) -> Result<Self, StorageError> {
         Ok(Self {

lib/tests/store.rs

@@ -312,14 +312,13 @@ fn test_backup() -> Result<(), Box<dyn Error>> {
         GraphNameRef::DefaultGraph,
     );
     let store_dir = TempDir::default();
-    let secondary_store_dir = TempDir::default();
     let backup_from_rw_dir = TempDir::default();
     let backup_from_ro_dir = TempDir::default();
     let backup_from_secondary_dir = TempDir::default();
 
     let store = Store::open(&store_dir)?;
     store.insert(quad)?;
-    let secondary_store = Store::open_secondary(&store_dir, secondary_store_dir)?;
+    let secondary_store = Store::open_secondary(&store_dir)?;
     store.flush()?;
 
     store.backup(&backup_from_rw_dir)?;
@@ -396,11 +395,10 @@ fn test_secondary() -> Result<(), Box<dyn Error>> {
         GraphNameRef::DefaultGraph,
     );
     let primary_dir = TempDir::default();
-    let secondary_dir = TempDir::default();
 
     // We open the store
     let primary = Store::open(&primary_dir)?;
-    let secondary = Store::open_secondary(&primary_dir, &secondary_dir)?;
+    let secondary = Store::open_secondary(&primary_dir)?;
 
     // We insert a quad
     primary.insert(quad)?;
@@ -434,12 +432,11 @@ fn test_secondary() -> Result<(), Box<dyn Error>> {
 #[cfg(not(target_family = "wasm"))]
 fn test_open_secondary_bad_dir() -> Result<(), Box<dyn Error>> {
     let primary_dir = TempDir::default();
-    let secondary_dir = TempDir::default();
     create_dir(&primary_dir.0)?;
     {
         File::create(primary_dir.0.join("CURRENT"))?.write_all(b"foo")?;
     }
-    assert!(Store::open_secondary(&primary_dir, &secondary_dir).is_err());
+    assert!(Store::open_secondary(&primary_dir).is_err());
     Ok(())
 }
 

server/src/main.rs

@@ -69,18 +69,20 @@ enum Command {
     },
     /// Start Oxigraph HTTP server in secondary mode.
     ///
-    /// It allows to read the database while other processes are accessing it.
+    /// It allows to read the database while an other process is writing it.
     /// Changes done while this process is running will be replicated after a possible lag.
     ///
     /// Beware: RocksDB secondary mode does not support snapshots and transactions.
     /// Dirty reads might happen.
     ServeSecondary {
         /// Directory where the primary Oxigraph instance is writing to.
-        #[arg(long)]
+        #[arg(long, alias = "location", short_alias = 'l')]
         primary_location: PathBuf,
         /// Directory to which the current secondary instance might write to.
+        ///
+        /// By default, temporary storage is used.
         #[arg(long)]
-        secondary_location: PathBuf,
+        secondary_location: Option<PathBuf>,
         /// Host and port to listen to.
         #[arg(short, long, default_value = "localhost:7878")]
         bind: String,
@@ -163,7 +165,11 @@ pub fn main() -> anyhow::Result<()> {
             secondary_location,
             bind,
         } => serve(
-            Store::open_secondary(primary_location, secondary_location)?,
+            if let Some(secondary_location) = secondary_location {
+                Store::open_persistent_secondary(primary_location, secondary_location)
+            } else {
+                Store::open_secondary(primary_location)
+            }?,
             bind,
             false,
         ),