vecindex: add Try methods to Store

Add a new set of Try methods to the Store method that run outside the scope of
a transaction. Each Try method checks one or two preconditions, and will only
perform its operation if the preconditions pass. These new methods will be used
to do background fixup processing without the use of transactions, in order to
reduce contention between foreground and background work.

In order to handle multiple racing workers, this commit introduces a new state
machine that tracks the progress of split and merge fixups. The current state
of a partition is stored in its metadata. Each Try method takes "expected"
metadata that represents a worker's current understanding of a partition's
state. If the actual metadata does not match the expected metadata, then
another worker must have updated it, and so the Try method fails with a
ConditionFailedError. The calling worker can reset its understanding of that
partition's state, and continue processing the fixup.

Epic: CRDB-42943

Release note: None

Author: andy-kimball

pkg/cmd/vecbench/mem_provider.go

@@ -233,13 +233,14 @@ func (m *MemProvider) ensureIndex(ctx context.Context) error {
 	if m.index != nil {
 		return nil
 	}
+
+	quantizer := quantize.NewRaBitQuantizer(m.dims, seed)
 	if m.store == nil {
 		// Construct empty store if one doesn't yet exist.
-		m.store = memstore.New(m.dims, seed)
+		m.store = memstore.New(quantizer, seed)
 	}
 
 	var err error
-	quantizer := quantize.NewRaBitQuantizer(m.dims, seed)
 	m.index, err = cspann.NewIndex(ctx, m.store, quantizer, seed, &m.options, m.stopper)
 	return err
 }

pkg/sql/vecindex/cspann/BUILD.bazel

@@ -19,9 +19,11 @@ go_library(
         "kmeans.go",
         "pacer.go",
         "partition.go",
+        "partition_metadata.go",
         "search_set.go",
         "split_data.go",
         "store.go",
+        "store_errors.go",
     ],
     embed = [":cspann_go_proto"],
     importpath = "github.com/cockroachdb/cockroach/pkg/sql/vecindex/cspann",
@@ -52,6 +54,7 @@ go_test(
         "index_test.go",
         "kmeans_test.go",
         "pacer_test.go",
+        "partition_metadata_test.go",
         "partition_test.go",
         "search_set_test.go",
     ],

pkg/sql/vecindex/cspann/commontest/BUILD.bazel

@@ -14,6 +14,7 @@ go_library(
         "//pkg/sql/vecindex/cspann/testutils",
         "//pkg/sql/vecindex/cspann/workspace",
         "//pkg/util/num32",
+        "//pkg/util/timeutil",
         "//pkg/util/vector",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_stretchr_testify//require",