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Merge pull request #379 from benbjohnson/tx-doc

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Add docs for dependent transactions.
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Ben Johnson 2015-05-21 09:53:52 -06:00
commit afceb316b9
2 changed files with 10 additions and 0 deletions
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5
README.md
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@ -87,6 +87,11 @@ are not thread safe. To work with data in multiple goroutines you must start
a transaction for each one or use locking to ensure only one goroutine accesses a transaction for each one or use locking to ensure only one goroutine accesses
a transaction at a time. Creating transaction from the `DB` is thread safe. a transaction at a time. Creating transaction from the `DB` is thread safe.
Read-only transactions and read-write transactions should not depend on one
another and generally shouldn't be opened simultaneously in the same goroutine.
This can cause a deadlock as the read-write transaction needs to periodically
re-map the data file but it cannot do so while a read-only transaction is open.
#### Read-write transactions #### Read-write transactions

5
db.go
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@ -401,6 +401,11 @@ func (db *DB) close() error {
// will cause the calls to block and be serialized until the current write // will cause the calls to block and be serialized until the current write
// transaction finishes. // 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 // IMPORTANT: You must close read-only transactions after you are finished or
// else the database will not reclaim old pages. // else the database will not reclaim old pages.
func (db *DB) Begin(writable bool) (*Tx, error) { func (db *DB) Begin(writable bool) (*Tx, error) {