Merge pull request #1429 from tigerbeetle/matklad/thinner-cache-map

state_machine: reduce memory usage by about 200 MiB
tigerbeetle · Jan 19, 2024 · f7cf98e · f7cf98e
2 parents f96a0a4 + a3eb0a7
commit f7cf98e
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Showing 3 changed files with 27 additions and 15 deletions.
diff --git a/src/lsm/groove.zig b/src/lsm/groove.zig
@@ -471,8 +471,10 @@ pub fn GrooveType(
         scan_builder: ScanBuilder,
 
         pub const Options = struct {
-            /// The maximum number of objects that might be prefetched by a batch.
-            prefetch_entries_max: u32,
+            /// The maximum number of objects that might be prefetched and not modified by a batch.
+            prefetch_entries_for_read_max: u32,
+            /// The maximum number of objects that might be prefetched and then modified by a batch.
+            prefetch_entries_for_update_max: u32,
             cache_entries_max: u32,
 
             tree_options_object: ObjectTree.Options,
@@ -491,9 +493,10 @@ pub fn GrooveType(
 
                 // In the worst case, each Map must be able to store the value_count_max (to
                 // contain either TableMutable or TableImmutable) as well as the maximum number of
-                // prefetches a bar may perform.
+                // prefetches a bar may perform, excluding prefetches already accounted for by
+                // value_count_max.
                 .map_value_count_max = @as(u32, ObjectTree.Table.value_count_max) +
-                    (options.prefetch_entries_max * constants.lsm_batch_multiple),
+                    (options.prefetch_entries_for_read_max * constants.lsm_batch_multiple),
 
                 // Scopes are limited to a single beat, so the maximum number of entries in a
                 // single scope is value_count_max / constants.lsm_batch_multiple.
@@ -554,7 +557,10 @@ pub fn GrooveType(
             }
 
             var prefetch_keys = PrefetchKeys{};
-            try prefetch_keys.ensureTotalCapacity(allocator, options.prefetch_entries_max);
+            try prefetch_keys.ensureTotalCapacity(
+                allocator,
+                options.prefetch_entries_for_read_max + options.prefetch_entries_for_update_max,
+            );
             errdefer prefetch_keys.deinit(allocator);
 
             var scan_builder = if (has_scan) try ScanBuilder.init(allocator) else {};

diff --git a/src/state_machine.zig b/src/state_machine.zig
@@ -1315,12 +1315,11 @@ pub fn StateMachineType(
 
             return .{
                 .accounts = .{
-                    .prefetch_entries_max = @max(
-                        // create_account()/lookup_account() looks up 1 AccountImmutable per item.
-                        batch_accounts_max,
-                        // create_transfer()/post_or_void_pending_transfer() looks up 2
-                        // AccountImmutables for every transfer.
-                        2 * batch_transfers_max,
+                    // lookup_account() looks up 1 AccountImmutable per item.
+                    .prefetch_entries_for_read_max = batch_accounts_max,
+                    .prefetch_entries_for_update_max = @max(
+                        batch_accounts_max, // create_account()
+                        2 * batch_transfers_max, // create_transfer(), debit and credit accounts
                     ),
                     .cache_entries_max = options.cache_entries_accounts,
                     .tree_options_object = .{},
@@ -1338,8 +1337,11 @@ pub fn StateMachineType(
                     },
                 },
                 .transfers = .{
-                    // *2 to fetch pending and post/void transfer.
-                    .prefetch_entries_max = 2 * batch_transfers_max,
+                    // lookup_transfer() looks up 1 Transfer.
+                    // create_transfer() looks up at most 1 Transfer for posting/voiding.
+                    .prefetch_entries_for_read_max = batch_transfers_max,
+                    // create_transfer() updates a single Transfer.
+                    .prefetch_entries_for_update_max = batch_transfers_max,
                     .cache_entries_max = options.cache_entries_transfers,
                     .tree_options_object = .{},
                     .tree_options_id = .{},
@@ -1357,7 +1359,10 @@ pub fn StateMachineType(
                     },
                 },
                 .posted = .{
-                    .prefetch_entries_max = batch_transfers_max,
+                    // Nothing lookups posted groove.
+                    .prefetch_entries_for_read_max = 0,
+                    // create_transfer() posts/voids at most one transfer.
+                    .prefetch_entries_for_update_max = batch_transfers_max,
                     .cache_entries_max = options.cache_entries_posted,
                     .tree_options_object = .{},
                     .tree_options_id = {},

diff --git a/src/testing/state_machine.zig b/src/testing/state_machine.zig
@@ -108,7 +108,8 @@ pub fn StateMachineType(
                 .{
                     .things = .{
                         .cache_entries_max = 2048,
-                        .prefetch_entries_max = 1,
+                        .prefetch_entries_for_read_max = 0,
+                        .prefetch_entries_for_update_max = 1,
                         .tree_options_object = .{},
                         .tree_options_id = .{},
                         .tree_options_index = .{ .value = .{} },