Add docs for dependent transactions.

This commit adds documentation to clarify that read-only and read-write
transactions should not be mixed in the same goroutine as it can cause
deadlocks during remapping.

See: https://github.com/boltdb/bolt/issues/378

1 files changed, 5 insertions, 0 deletions

diff --git a/db.go b/db.go
index f5ca05e..d39c4aa 100644
--- a/db.go
+++ b/db.go
@@ -401,6 +401,11 @@ func (db *DB) close() error {
 // will cause the calls to block and be serialized until the current write
 // transaction finishes.
 //
+// Transactions should not be depedent on one another. Opening a read
+// transaction and a write transaction in the same goroutine can cause the
+// writer to deadlock because the database periodically needs to re-mmap itself
+// as it grows and it cannot do that while a read transaction is open.
+//
 // IMPORTANT: You must close read-only transactions after you are finished or
 // else the database will not reclaim old pages.
 func (db *DB) Begin(writable bool) (*Tx, error) {