diff options
Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 42 |
1 files changed, 42 insertions, 0 deletions
@@ -125,6 +125,48 @@ no mutating operations are allowed within a read-only transaction. You can only retrieve buckets, retrieve values, and copy the database within a read-only transaction. + +#### Batch read-write transactions + +Each `DB.Update()` waits for disk to commit the writes. This overhead +can be minimized by combining multiple updates with the `DB.Batch()` +function: + +```go +err := db.Batch(func(tx *bolt.Tx) error { + ... + return nil +}) +``` + +Concurrent Batch calls are opportunistically combined into larger +transactions. Batch is only useful when there are multiple goroutines +calling it. + +The trade-off is that `Batch` can call the given +function multiple times, if parts of the transaction fail. The +function must be idempotent and side effects must take effect only +after a successful return from `DB.Batch()`. + +For example: don't display messages from inside the function, instead +set variables in the enclosing scope: + +```go +var id uint64 +err := db.Batch(func(tx *bolt.Tx) error { + // Find last key in bucket, decode as bigendian uint64, increment + // by one, encode back to []byte, and add new key. + ... + id = newValue + return nil +}) +if err != nil { + return ... +} +fmt.Println("Allocated ID %d", id) +``` + + #### Managing transactions manually The `DB.View()` and `DB.Update()` functions are wrappers around the `DB.Begin()` |