@@ -17,4 +17,6 @@ mod tables;
 mod traits;
 
 pub use tables::{ALL_TABLES, Table};
-pub use traits::{Error, PrefixResult, StorageBackend, StorageReadView, StorageWriteBatch};
+pub use traits::{
+    Error, PrefixResult, StorageBackend, StorageReadView, StorageReadViewExt, StorageWriteBatch,
+};
@@ -24,8 +24,38 @@ pub trait StorageBackend: Send + Sync {
 
 /// A read-only view of the storage.
 pub trait StorageReadView {
-    /// Get a value by key from a table.
-    fn get(&self, table: Table, key: &[u8]) -> Result<Option<Vec<u8>>, Error>;
+    /// Calls `read_fn` with a borrow of the value stored under `key`, if any,
+    /// and returns whether the key was present.
+    ///
+    /// The value is never copied: `read_fn` sees the backend's own buffer, so
+    /// a caller that only decodes or inspects the bytes avoids allocating a
+    /// value-sized `Vec` (full state snapshots are 100+ MB on mainnet-sized
+    /// beacon chains). `read_fn` runs at most once, and its error is returned
+    /// as-is. A `&mut dyn FnMut` rather than a generic closure, so the trait
+    /// stays usable as `dyn StorageReadView`.
+    fn read(
+        &self,
+        table: Table,
+        key: &[u8],
+        read_fn: &mut dyn FnMut(&[u8]) -> Result<(), Error>,
+    ) -> Result<bool, Error>;
+
+    /// Get a value by key from a table, copied into an owned `Vec`.
+    ///
+    /// Prefer [`StorageReadViewExt::read_with`] when the bytes are only
+    /// decoded: it decodes from the backend's buffer without the copy.
+    fn get(&self, table: Table, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
+        self.read_with(table, key, <[u8]>::to_vec)
+    }
+
+    /// Whether `key` is present in a table.
+    ///
+    /// Same answer as `get(..)?.is_some()` but never materializes the value, so
+    /// the cost does not scale with its size. Prefer it for pure existence
+    /// checks on large values.
+    fn contains(&self, table: Table, key: &[u8]) -> Result<bool, Error> {
+        self.read(table, key, &mut |_| Ok(()))
+    }
 
     /// Iterate over all entries with a given key prefix.
     fn prefix_iterator(
@@ -35,6 +65,33 @@ pub trait StorageReadView {
     ) -> Result<Box<dyn Iterator<Item = PrefixResult> + '_>, Error>;
 }
 
+/// Generic conveniences over [`StorageReadView::read`].
+///
+/// A separate trait because its methods are generic, which would make
+/// `StorageReadView` itself unusable as a trait object. The blanket impl
+/// covers every view, `dyn StorageReadView` included.
+pub trait StorageReadViewExt: StorageReadView {
+    /// Decodes the value stored under `key` straight from the backend's
+    /// buffer, without copying it first. `None` when the key is absent.
+    fn read_with<T>(
+        &self,
+        table: Table,
+        key: &[u8],
+        decode: impl FnOnce(&[u8]) -> T,
+    ) -> Result<Option<T>, Error> {
+        let mut decode = Some(decode);
+        let mut value = None;
+        self.read(table, key, &mut |bytes| {
+            let decode = decode.take().expect("read calls read_fn at most once");
+            value = Some(decode(bytes));
+            Ok(())
+        })?;
+        Ok(value)
+    }
+}
+
+impl<V: StorageReadView + ?Sized> StorageReadViewExt for V {}
+
 /// A write batch that can be committed atomically.
 pub trait StorageWriteBatch: Send {
     /// Put multiple key-value pairs into a table.
 
@@ -66,13 +66,17 @@ struct InMemoryReadView<'a> {
 }
 
 impl StorageReadView for InMemoryReadView<'_> {
-    fn get(&self, table: Table, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
-        Ok(self
-            .guard
-            .get(&table)
-            .expect("table exists")
-            .get(key)
-            .cloned())
+    fn read(
+        &self,
+        table: Table,
+        key: &[u8],
+        read_fn: &mut dyn FnMut(&[u8]) -> Result<(), Error>,
+    ) -> Result<bool, Error> {
+        let Some(value) = self.guard.get(&table).expect("table exists").get(key) else {
+            return Ok(false);
+        };
+        read_fn(value)?;
+        Ok(true)
     }
 
     fn prefix_iterator(
 
@@ -4,8 +4,8 @@ use crate::api::{
     ALL_TABLES, Error, PrefixResult, StorageBackend, StorageReadView, StorageWriteBatch, Table,
 };
 use rocksdb::{
-    BlockBasedOptions, Cache, ColumnFamilyDescriptor, DBWithThreadMode, MultiThreaded, Options,
-    WriteBatch, WriteOptions,
+    BlockBasedOptions, Cache, ColumnFamilyDescriptor, DBCompressionType, DBWithThreadMode,
+    MultiThreaded, Options, WriteBatch, WriteOptions,
 };
 use std::path::Path;
 use std::sync::Arc;
@@ -18,6 +18,43 @@ fn cf_name(table: Table) -> &'static str {
     table.name()
 }
 
+/// The smallest value a blob-file table stores out of line.
+///
+/// RocksDB's default data block size: a larger value would get an oversized
+/// block of its own anyway, so it gains nothing from staying inline.
+const MIN_BLOB_SIZE: u64 = 4 * 1024;
+
+/// Whether a table keeps its values in blob files rather than inline in SSTs.
+///
+/// `States` holds full state snapshots (100+ MB on mainnet-sized beacon
+/// chains) and `StateDiffs` the deltas between them (hundreds of KB). Inline,
+/// every compaction that touches a file rewrites those values, and a lookup
+/// that misses still reads the data block around the key, which here can be
+/// a whole snapshot. In a blob file a value is written once, and the SSTs
+/// hold only small references to it.
+fn stores_values_in_blob_files(table: Table) -> bool {
+    matches!(table, Table::States | Table::StateDiffs)
+}
+
+/// Moves a column family's large values into blob files.
+///
+/// RocksDB applies the change to an existing database as it goes: new
+/// writes land in blob files, and inline values move out as compaction
+/// rewrites their SSTs. So a data directory written without it opens
+/// unchanged, and no `DB_VERSION` bump is needed.
+fn enable_blob_files(cf_opts: &mut Options) {
+    cf_opts.set_enable_blob_files(true);
+    cf_opts.set_min_blob_size(MIN_BLOB_SIZE);
+    // SST blocks get RocksDB's default Snappy, but blob files default to no
+    // compression, so moving the values out would otherwise grow the tables
+    // on disk. The values are raw SSZ.
+    cf_opts.set_blob_compression_type(DBCompressionType::Lz4);
+    // No blob garbage collection: nothing deletes or overwrites a state, so it
+    // would only relocate live blobs during compaction. Revisit if states are
+    // ever pruned. No blob cache either: the store caches decoded states
+    // itself, and a snapshot-sized entry would evict the whole block cache.
+}
+
 /// RocksDB storage backend.
 #[derive(Clone)]
 pub struct RocksDBBackend {
@@ -52,6 +89,9 @@ impl RocksDBBackend {
             .map(|t| {
                 let mut cf_opts = Options::default();
                 cf_opts.set_block_based_table_factory(&block_opts);
+                if stores_values_in_blob_files(*t) {
+                    enable_blob_files(&mut cf_opts);
+                }
                 ColumnFamilyDescriptor::new(cf_name(*t), cf_opts)
             })
             .collect();
@@ -93,7 +133,15 @@ impl StorageBackend for RocksDBBackend {
             .ok()
             .flatten()
             .unwrap_or(0);
-        sst_bytes + memtable_bytes
+        // `estimate-live-data-size` counts SST files only, so a blob-file
+        // table's values would otherwise vanish from the estimate.
+        let blob_bytes = self
+            .db
+            .property_int_value_cf(&cf, "rocksdb.live-blob-file-size")
+            .ok()
+            .flatten()
+            .unwrap_or(0);
+        sst_bytes + memtable_bytes + blob_bytes
     }
 }
 
@@ -103,13 +151,24 @@ struct RocksDBReadView {
 }
 
 impl StorageReadView for RocksDBReadView {
-    fn get(&self, table: Table, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
+    fn read(
+        &self,
+        table: Table,
+        key: &[u8],
+        read_fn: &mut dyn FnMut(&[u8]) -> Result<(), Error>,
+    ) -> Result<bool, Error> {
         let cf = self
             .db
             .cf_handle(cf_name(table))
             .ok_or_else(|| format!("Column family {} not found", cf_name(table)))?;
 
-        Ok(self.db.get_cf(&cf, key)?)
+        // Pinned: references RocksDB's own buffer instead of copying the
+        // value into a `Vec`.
+        let Some(value) = self.db.get_pinned_cf(&cf, key)? else {
+            return Ok(false);
+        };
+        read_fn(&value)?;
+        Ok(true)
     }
 
     fn prefix_iterator(
@@ -200,6 +259,82 @@ mod tests {
         run_backend_tests(&backend);
     }
 
+    /// A value big enough for a blob file, and the property counting them.
+    const BLOB_VALUE_LEN: usize = 64 * 1024;
+    const NUM_BLOB_FILES: &str = "rocksdb.num-blob-files";
+
+    fn num_blob_files(backend: &RocksDBBackend, table: Table) -> u64 {
+        let cf = backend.db.cf_handle(cf_name(table)).unwrap();
+        backend
+            .db
+            .property_int_value_cf(&cf, NUM_BLOB_FILES)
+            .unwrap()
+            .unwrap()
+    }
+
+    fn put_and_flush(backend: &RocksDBBackend, table: Table, key: &[u8], value: Vec<u8>) {
+        let mut batch = backend.begin_write().unwrap();
+        batch.put_batch(table, vec![(key.to_vec(), value)]).unwrap();
+        batch.commit().unwrap();
+        let cf = backend.db.cf_handle(cf_name(table)).unwrap();
+        backend.db.flush_cf(&cf).unwrap();
+    }
+
+    #[test]
+    fn large_state_values_live_in_blob_files() {
+        let dir = tempdir().unwrap();
+        let backend = RocksDBBackend::open(dir.path()).unwrap();
+        let value: Vec<u8> = (0..BLOB_VALUE_LEN).map(|i| (i % 251) as u8).collect();
+
+        for table in [Table::States, Table::StateDiffs] {
+            put_and_flush(&backend, table, b"big", value.clone());
+            assert_eq!(num_blob_files(&backend, table), 1, "{table:?}");
+
+            let view = backend.begin_read().unwrap();
+            assert_eq!(view.get(table, b"big").unwrap(), Some(value.clone()));
+            assert!(view.contains(table, b"big").unwrap());
+            assert!(!view.contains(table, b"absent").unwrap());
+        }
+        assert!(backend.estimate_table_bytes(Table::States) > 0);
+
+        // Small values, and every other table, stay inline.
+        put_and_flush(&backend, Table::States, b"small", vec![7; 16]);
+        assert_eq!(num_blob_files(&backend, Table::States), 1);
+        put_and_flush(&backend, Table::BlockHeaders, b"big", value);
+        assert_eq!(num_blob_files(&backend, Table::BlockHeaders), 0);
+    }
+
+    #[test]
+    fn a_directory_written_without_blob_files_still_reads() {
+        let dir = tempdir().unwrap();
+        let value: Vec<u8> = (0..BLOB_VALUE_LEN).map(|i| (i % 251) as u8).collect();
+
+        // The layout a data directory had before blob files: every table
+        // with plain options.
+        {
+            let mut opts = Options::default();
+            opts.create_if_missing(true);
+            opts.create_missing_column_families(true);
+            let cfs = ALL_TABLES.iter().map(|t| cf_name(*t));
+            let db = DBWithThreadMode::<MultiThreaded>::open_cf(&opts, dir.path(), cfs).unwrap();
+            let cf = db.cf_handle(cf_name(Table::States)).unwrap();
+            db.put_cf(&cf, b"old", &value).unwrap();
+            db.flush_cf(&cf).unwrap();
+        }
+
+        let backend = RocksDBBackend::open(dir.path()).unwrap();
+        assert_eq!(num_blob_files(&backend, Table::States), 0);
+        put_and_flush(&backend, Table::States, b"new", value.clone());
+        assert_eq!(num_blob_files(&backend, Table::States), 1);
+
+        let view = backend.begin_read().unwrap();
+        assert_eq!(
+            view.get(Table::States, b"old").unwrap(),
+            Some(value.clone())
+        );
+        assert_eq!(view.get(Table::States, b"new").unwrap(), Some(value));
+    }
+
     #[test]
     fn test_persistence() {
         let dir = tempdir().unwrap();
 
@@ -17,6 +17,8 @@ pub fn run_backend_tests(backend: &dyn StorageBackend) {
     test_delete(backend);
     test_prefix_iterator(backend);
     test_nonexistent_key(backend);
+    test_contains(backend);
+    test_read(backend);
     test_delete_then_put(backend);
     test_put_then_delete(backend);
     test_delete_range(backend);
@@ -45,6 +47,72 @@ fn test_put_and_get(backend: &dyn StorageBackend) {
     }
 }
 
+fn test_contains(backend: &dyn StorageBackend) {
+    {
+        let mut batch = backend.begin_write().unwrap();
+        batch
+            .put_batch(
+                Table::BlockHeaders,
+                vec![(b"test_contains_key".to_vec(), b"value1".to_vec())],
+            )
+            .unwrap();
+        batch.commit().unwrap();
+    }
+    let view = backend.begin_read().unwrap();
+    assert!(
+        view.contains(Table::BlockHeaders, b"test_contains_key")
+            .unwrap()
+    );
+    assert!(
+        !view
+            .contains(Table::BlockHeaders, b"test_contains_missing")
+            .unwrap()
+    );
+}
+
+fn test_read(backend: &dyn StorageBackend) {
+    {
+        let mut batch = backend.begin_write().unwrap();
+        batch
+            .put_batch(
+                Table::BlockHeaders,
+                vec![(b"test_read_key".to_vec(), b"value1".to_vec())],
+            )
+            .unwrap();
+        batch.commit().unwrap();
+    }
+    let view = backend.begin_read().unwrap();
+
+    let mut seen = Vec::new();
+    let found = view
+        .read(Table::BlockHeaders, b"test_read_key", &mut |bytes| {
+            seen.push(bytes.to_vec());
+            Ok(())
+        })
+        .unwrap();
+    assert!(found);
+    assert_eq!(seen, vec![b"value1".to_vec()]);
+
+    // A missing key never reaches the callback.
+    let mut calls = 0;
+    let found = view
+        .read(Table::BlockHeaders, b"test_read_missing", &mut |_| {
+            calls += 1;
+            Ok(())
+        })
+        .unwrap();
+    assert!(!found);
+    assert_eq!(calls, 0);
+
+    // The callback's own error is what `read` returns.
+    let err = view
+        .read(Table::BlockHeaders, b"test_read_key", &mut |_| {
+            Err("decode failed".into())
+        })
+        .unwrap_err();
+    assert_eq!(err.to_string(), "decode failed");
+}
+
 fn test_delete(backend: &dyn StorageBackend) {
     // Write data
     {
 
@@ -9,7 +9,9 @@ mod state_diff;
 mod state_writer;
 mod store;
 
-pub use api::{ALL_TABLES, StorageBackend, StorageReadView, StorageWriteBatch, Table};
+pub use api::{
+    ALL_TABLES, StorageBackend, StorageReadView, StorageReadViewExt, StorageWriteBatch, Table,
+};
 pub use committee_cache::{CommitteeCache, Lookup, ShufflingKey};
 /// Error type returned by the fallible [`Store`] operations, exported so
 /// callers can match on it (e.g. to distinguish [`Error::DbVersionMismatch`]).