[TieredStorage] Store account address range (solana-labs#172)

#### Problem
The TieredStorageFooter has the min_account_address and
max_account_address fields to describe the account address
range in its file.  But the current implementation hasn't updated
the fields yet.

#### Summary of Changes
This PR enables the TieredStorage to persist address range
information into its footer via min_account_address and
max_account_address.

#### Test Plan
Updated tiered-storage test to verify persisted account address range.

accounts-db/src/tiered_storage.rs

@@ -183,7 +183,7 @@ mod tests {
             mem::ManuallyDrop,
         },
         tempfile::tempdir,
-        test_utils::{create_test_account, verify_test_account},
+        test_utils::{create_test_account, verify_test_account_with_footer},
     };
 
     impl TieredStorage {
@@ -368,13 +368,33 @@ mod tests {
 
         let mut index_offset = IndexOffset(0);
         let mut verified_accounts = HashSet::new();
+        let footer = reader.footer();
+
+        const MIN_PUBKEY: Pubkey = Pubkey::new_from_array([0x00u8; 32]);
+        const MAX_PUBKEY: Pubkey = Pubkey::new_from_array([0xFFu8; 32]);
+        let mut min_pubkey_ref = &MAX_PUBKEY;
+        let mut max_pubkey_ref = &MIN_PUBKEY;
+
         while let Some((stored_meta, next)) = reader.get_account(index_offset).unwrap() {
             if let Some(account) = expected_accounts_map.get(stored_meta.pubkey()) {
-                verify_test_account(&stored_meta, *account, stored_meta.pubkey());
+                verify_test_account_with_footer(
+                    &stored_meta,
+                    *account,
+                    stored_meta.pubkey(),
+                    footer,
+                );
                 verified_accounts.insert(stored_meta.pubkey());
+                if *min_pubkey_ref > *stored_meta.pubkey() {
+                    min_pubkey_ref = stored_meta.pubkey();
+                }
+                if *max_pubkey_ref < *stored_meta.pubkey() {
+                    max_pubkey_ref = stored_meta.pubkey();
+                }
             }
             index_offset = next;
         }
+        assert_eq!(footer.min_account_address, *min_pubkey_ref);
+        assert_eq!(footer.max_account_address, *max_pubkey_ref);
         assert!(!verified_accounts.is_empty());
         assert_eq!(verified_accounts.len(), expected_accounts_map.len())
     }

accounts-db/src/tiered_storage/hot.rs

@@ -10,7 +10,9 @@ use {
             file::{TieredReadableFile, TieredWritableFile},
             footer::{AccountBlockFormat, AccountMetaFormat, TieredStorageFooter},
             index::{AccountIndexWriterEntry, AccountOffset, IndexBlockFormat, IndexOffset},
-            meta::{AccountMetaFlags, AccountMetaOptionalFields, TieredAccountMeta},
+            meta::{
+                AccountAddressRange, AccountMetaFlags, AccountMetaOptionalFields, TieredAccountMeta,
+            },
             mmap_utils::{get_pod, get_slice},
             owners::{OwnerOffset, OwnersBlockFormat, OwnersTable, OWNER_NO_OWNER},
             StorableAccounts, StorableAccountsWithHashesAndWriteVersions, TieredStorageError,
@@ -620,6 +622,7 @@ impl HotStorageWriter {
         let mut index = vec![];
         let mut owners_table = OwnersTable::default();
         let mut cursor = 0;
+        let mut address_range = AccountAddressRange::default();
 
         // writing accounts blocks
         let len = accounts.accounts.len();
@@ -631,6 +634,7 @@ impl HotStorageWriter {
                 address,
                 offset: HotAccountOffset::new(cursor)?,
             };
+            address_range.update(address);
 
             // Obtain necessary fields from the account, or default fields
             // for a zero-lamport account in the None case.
@@ -691,7 +695,8 @@ impl HotStorageWriter {
         footer
             .owners_block_format
             .write_owners_block(&mut self.storage, &owners_table)?;
-
+        footer.min_account_address = *address_range.min;
+        footer.max_account_address = *address_range.max;
         footer.write_footer_block(&mut self.storage)?;
 
         Ok(stored_infos)

accounts-db/src/tiered_storage/meta.rs

@@ -4,7 +4,7 @@ use {
     crate::tiered_storage::owners::OwnerOffset,
     bytemuck::{Pod, Zeroable},
     modular_bitfield::prelude::*,
-    solana_sdk::stake_history::Epoch,
+    solana_sdk::{pubkey::Pubkey, stake_history::Epoch},
 };
 
 /// The struct that handles the account meta flags.
@@ -124,6 +124,38 @@ impl AccountMetaOptionalFields {
     }
 }
 
+const MIN_ACCOUNT_ADDRESS: Pubkey = Pubkey::new_from_array([0x00u8; 32]);
+const MAX_ACCOUNT_ADDRESS: Pubkey = Pubkey::new_from_array([0xFFu8; 32]);
+
+#[derive(Debug)]
+/// A struct that maintains an address-range using its min and max fields.
+pub struct AccountAddressRange<'a> {
+    /// The minimum address observed via update()
+    pub min: &'a Pubkey,
+    /// The maximum address observed via update()
+    pub max: &'a Pubkey,
+}
+
+impl Default for AccountAddressRange<'_> {
+    fn default() -> Self {
+        Self {
+            min: &MAX_ACCOUNT_ADDRESS,
+            max: &MIN_ACCOUNT_ADDRESS,
+        }
+    }
+}
+
+impl<'a> AccountAddressRange<'a> {
+    pub fn update(&mut self, address: &'a Pubkey) {
+        if *self.min > *address {
+            self.min = address;
+        }
+        if *self.max < *address {
+            self.max = address;
+        }
+    }
+}
+
 #[cfg(test)]
 pub mod tests {
     use super::*;
@@ -221,4 +253,47 @@ pub mod tests {
             );
         }
     }
+
+    #[test]
+    fn test_pubkey_range_update_single() {
+        let address = solana_sdk::pubkey::new_rand();
+        let mut address_range = AccountAddressRange::default();
+
+        address_range.update(&address);
+        // For a single update, the min and max should equal to the address
+        assert_eq!(*address_range.min, address);
+        assert_eq!(*address_range.max, address);
+    }
+
+    #[test]
+    fn test_pubkey_range_update_multiple() {
+        const NUM_PUBKEYS: usize = 20;
+
+        let mut address_range = AccountAddressRange::default();
+        let mut addresses = Vec::with_capacity(NUM_PUBKEYS);
+
+        let mut min_index = 0;
+        let mut max_index = 0;
+
+        // Generate random addresses and track expected min and max indices
+        for i in 0..NUM_PUBKEYS {
+            let address = solana_sdk::pubkey::new_rand();
+            addresses.push(address);
+
+            // Update expected min and max indices
+            if address < addresses[min_index] {
+                min_index = i;
+            }
+            if address > addresses[max_index] {
+                max_index = i;
+            }
+        }
+
+        addresses
+            .iter()
+            .for_each(|address| address_range.update(address));
+
+        assert_eq!(*address_range.min, addresses[min_index]);
+        assert_eq!(*address_range.max, addresses[max_index]);
+    }
 }

accounts-db/src/tiered_storage/test_utils.rs

@@ -1,6 +1,7 @@
 #![cfg(test)]
 //! Helper functions for TieredStorage tests
 use {
+    super::footer::TieredStorageFooter,
     crate::{
         account_storage::meta::{StoredAccountMeta, StoredMeta},
         accounts_hash::AccountHash,
@@ -61,3 +62,14 @@ pub(super) fn verify_test_account(
     assert_eq!(stored_meta.pubkey(), address);
     assert_eq!(*stored_meta.hash(), AccountHash(Hash::default()));
 }
+
+pub(super) fn verify_test_account_with_footer(
+    stored_meta: &StoredAccountMeta<'_>,
+    account: Option<&impl ReadableAccount>,
+    address: &Pubkey,
+    footer: &TieredStorageFooter,
+) {
+    verify_test_account(stored_meta, account, address);
+    assert!(footer.min_account_address <= *address);
+    assert!(footer.max_account_address >= *address);
+}