Allow Blockstore to open unknown columns (#34174)

As we develop new features or modifications, we occassionally need to
introduce new columns to the Blockstore. Adding a new column introduces
a compatibility break given that opening the database in Primary mode
(R/W access) requires opening all columns. Reverting to an old software
version that is unaware of the new column is obviously problematic.

In the past, we have addressed by backporting minimal "stub" PR's to
older versions. This is annoying, and only allow compatibility for the
single version or two that we backport to.

This PR adds a change to automatically detect all columns, and create
default column descriptors for columns we were unaware of. As a result,
older software versions can open a Blockstore that was modified by a
newer software version, even if that new version added columns that the
old version is unaware of.

ledger/src/blockstore_db.rs

@@ -35,7 +35,7 @@ use {
     },
     solana_storage_proto::convert::generated,
     std::{
-        collections::HashMap,
+        collections::{HashMap, HashSet},
         ffi::{CStr, CString},
         fs,
         marker::PhantomData,
@@ -419,7 +419,7 @@ impl Rocks {
         }
         let oldest_slot = OldestSlot::default();
         let column_options = options.column_options.clone();
-        let cf_descriptors = Self::cf_descriptors(&options, &oldest_slot);
+        let cf_descriptors = Self::cf_descriptors(path, &options, &oldest_slot);
 
         // Open the database
         let db = match access_type {
@@ -454,15 +454,25 @@ impl Rocks {
         Ok(rocks)
     }
 
+    /// Create the column family (CF) descriptors necessary to open the database.
+    ///
+    /// In order to open a RocksDB database with Primary access, all columns must be opened. So,
+    /// in addition to creating descriptors for all of the expected columns, also create
+    /// descriptors for columns that were discovered but are otherwise unknown to the software.
+    ///
+    /// One case where columns could be unknown is if a RocksDB database is modified with a newer
+    /// software version that adds a new column, and then also opened with an older version that
+    /// did not have knowledge of that new column.
     fn cf_descriptors(
+        path: &Path,
         options: &BlockstoreOptions,
         oldest_slot: &OldestSlot,
     ) -> Vec<ColumnFamilyDescriptor> {
         use columns::*;
 
         let (cf_descriptor_shred_data, cf_descriptor_shred_code) =
             new_cf_descriptor_pair_shreds::<ShredData, ShredCode>(options, oldest_slot);
-        vec![
+        let mut cf_descriptors = vec![
             new_cf_descriptor::<SlotMeta>(options, oldest_slot),
             new_cf_descriptor::<DeadSlots>(options, oldest_slot),
             new_cf_descriptor::<DuplicateSlots>(options, oldest_slot),
@@ -484,7 +494,52 @@ impl Rocks {
             new_cf_descriptor::<ProgramCosts>(options, oldest_slot),
             new_cf_descriptor::<OptimisticSlots>(options, oldest_slot),
             new_cf_descriptor::<MerkleRootMeta>(options, oldest_slot),
-        ]
+        ];
+
+        // If the access type is Secondary, we don't need to open all of the
+        // columns so we can just return immediately.
+        match options.access_type {
+            AccessType::Secondary => {
+                return cf_descriptors;
+            }
+            AccessType::Primary | AccessType::PrimaryForMaintenance => {}
+        }
+
+        // Attempt to detect the column families that are present. It is not a
+        // fatal error if we cannot, for example, if the Blockstore is brand
+        // new and will be created by the call to Rocks::open().
+        let detected_cfs = match DB::list_cf(&Options::default(), path) {
+            Ok(detected_cfs) => detected_cfs,
+            Err(err) => {
+                warn!("Unable to detect Rocks columns: {err:?}");
+                vec![]
+            }
+        };
+        // The default column is handled automatically, we don't need to create
+        // a descriptor for it
+        const DEFAULT_COLUMN_NAME: &str = "default";
+        let known_cfs: HashSet<_> = cf_descriptors
+            .iter()
+            .map(|cf_descriptor| cf_descriptor.name().to_string())
+            .chain(std::iter::once(DEFAULT_COLUMN_NAME.to_string()))
+            .collect();
+        detected_cfs.iter().for_each(|cf_name| {
+            if known_cfs.get(cf_name.as_str()).is_none() {
+                info!("Detected unknown column {cf_name}, opening column with basic options");
+                // This version of the software was unaware of the column, so
+                // it is fair to assume that we will not attempt to read or
+                // write the column. So, set some bare bones settings to avoid
+                // using extra resources on this unknown column.
+                let mut options = Options::default();
+                // Lower the default to avoid unnecessary allocations
+                options.set_write_buffer_size(1024 * 1024);
+                // Disable compactions to avoid any modifications to the column
+                options.set_disable_auto_compactions(true);
+                cf_descriptors.push(ColumnFamilyDescriptor::new(cf_name, options));
+            }
+        });
+
+        cf_descriptors
     }
 
     fn columns() -> Vec<&'static str> {
@@ -2164,7 +2219,9 @@ fn should_enable_compression<C: 'static + Column + ColumnName>() -> bool {
 
 #[cfg(test)]
 pub mod tests {
-    use {super::*, crate::blockstore_db::columns::ShredData};
+    use {
+        super::*, crate::blockstore_db::columns::ShredData, std::path::PathBuf, tempfile::tempdir,
+    };
 
     #[test]
     fn test_compaction_filter() {
@@ -2217,14 +2274,15 @@ pub mod tests {
 
     #[test]
     fn test_cf_names_and_descriptors_equal_length() {
+        let path = PathBuf::default();
         let options = BlockstoreOptions::default();
         let oldest_slot = OldestSlot::default();
         // The names and descriptors don't need to be in the same order for our use cases;
         // however, there should be the same number of each. For example, adding a new column
         // should update both lists.
         assert_eq!(
             Rocks::columns().len(),
-            Rocks::cf_descriptors(&options, &oldest_slot).len()
+            Rocks::cf_descriptors(&path, &options, &oldest_slot).len()
         );
     }
 
@@ -2249,6 +2307,49 @@ pub mod tests {
         assert!(!should_enable_cf_compaction("something else"));
     }
 
+    #[test]
+    fn test_open_unknown_columns() {
+        solana_logger::setup();
+
+        let temp_dir = tempdir().unwrap();
+        let db_path = temp_dir.path();
+
+        // Open with Primary to create the new database
+        {
+            let options = BlockstoreOptions {
+                access_type: AccessType::Primary,
+                enforce_ulimit_nofile: false,
+                ..BlockstoreOptions::default()
+            };
+            let mut rocks = Rocks::open(db_path, options).unwrap();
+
+            // Introduce a new column that will not be known
+            rocks
+                .db
+                .create_cf("new_column", &Options::default())
+                .unwrap();
+        }
+
+        // Opening with either Secondary or Primary access should succeed,
+        // even though the Rocks code is unaware of "new_column"
+        {
+            let options = BlockstoreOptions {
+                access_type: AccessType::Secondary,
+                enforce_ulimit_nofile: false,
+                ..BlockstoreOptions::default()
+            };
+            let _ = Rocks::open(db_path, options).unwrap();
+        }
+        {
+            let options = BlockstoreOptions {
+                access_type: AccessType::Primary,
+                enforce_ulimit_nofile: false,
+                ..BlockstoreOptions::default()
+            };
+            let _ = Rocks::open(db_path, options).unwrap();
+        }
+    }
+
     impl<C> LedgerColumn<C>
     where
         C: ColumnIndexDeprecation + ProtobufColumn + ColumnName,