Add transaction batching

DB.Batch makes it easy to make lots of small transactions with
significantly better performance. Batch combines multiple concurrent
Update calls into a single disk transaction, managing errors smartly.

1 files changed, 29 insertions, 0 deletions

diff --git a/db.go b/db.go
index 4775850..d4c85fb 100644
--- a/db.go
+++ b/db.go
@@ -27,6 +27,12 @@ const magic uint32 = 0xED0CDAED
 // must be synchronzied using the msync(2) syscall.
 const IgnoreNoSync = runtime.GOOS == "openbsd"
 
+// Default values if not set in a DB instance.
+const (
+	DefaultMaxBatchSize  int = 1000
+	DefaultMaxBatchDelay     = 10 * time.Millisecond
+)
+
 // DB represents a collection of buckets persisted to a file on disk.
 // All data access is performed through transactions which can be obtained through the DB.
 // All the functions on DB will return a ErrDatabaseNotOpen if accessed before Open() is called.
@@ -49,6 +55,22 @@ type DB struct {
 	// THIS IS UNSAFE. PLEASE USE WITH CAUTION.
 	NoSync bool
 
+	// MaxBatchSize is the maximum size of a batch. Default value is
+	// copied from DefaultMaxBatchSize in Open.
+	//
+	// If <=0, disables batching.
+	//
+	// Do not change concurrently with calls to Batch.
+	MaxBatchSize int
+
+	// MaxBatchDelay is the maximum delay before a batch starts.
+	// Default value is copied from DefaultMaxBatchDelay in Open.
+	//
+	// If <=0, effectively disables batching.
+	//
+	// Do not change concurrently with calls to Batch.
+	MaxBatchDelay time.Duration
+
 	path     string
 	file     *os.File
 	dataref  []byte
@@ -63,6 +85,9 @@ type DB struct {
 	freelist *freelist
 	stats    Stats
 
+	batchMu sync.Mutex
+	batch   *batch
+
 	rwlock   sync.Mutex   // Allows only one writer at a time.
 	metalock sync.Mutex   // Protects meta page access.
 	mmaplock sync.RWMutex // Protects mmap access during remapping.
@@ -99,6 +124,10 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 		options = DefaultOptions
 	}
 
+	// Set default values for later DB operations.
+	db.MaxBatchSize = DefaultMaxBatchSize
+	db.MaxBatchDelay = DefaultMaxBatchDelay
+
 	// Open data file and separate sync handler for metadata writes.
 	db.path = path