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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 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 @@ -446,6 +451,21 @@ It's also useful to pipe these stats to a service such as statsd for monitoring or to provide an HTTP endpoint that will perform a fixed-length sample. +### Read-Only Mode + +Sometimes it is useful to create a shared, read-only Bolt database. To this, +set the `Options.ReadOnly` flag when opening your database. Read-only mode +uses a shared lock to allow multiple processes to read from the database but +it will block any processes from opening the database in read-write mode. + +```go +db, err := bolt.Open("my.db", 0666, &bolt.Options{ReadOnly: true}) +if err != nil { + log.Fatal(err) +} +``` + + ## Resources For more information on getting started with Bolt, check out the following articles: @@ -593,5 +613,7 @@ Below is a list of public, open source projects that use Bolt: * [Seaweed File System](https://github.com/chrislusf/weed-fs) - Highly scalable distributed key~file system with O(1) disk read. * [InfluxDB](http://influxdb.com) - Scalable datastore for metrics, events, and real-time analytics. * [Freehold](http://tshannon.bitbucket.org/freehold/) - An open, secure, and lightweight platform for your files and data. +* [Prometheus Annotation Server](https://github.com/oliver006/prom_annotation_server) - Annotation server for PromDash & Prometheus service monitoring system. +* [Consul](https://github.com/hashicorp/consul) - Consul is service discovery and configuration made easy. Distributed, highly available, and datacenter-aware. If you are using Bolt in a project please send a pull request to add it to the list. |