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gocql

Build GoDoc

This is a fork of gocql package that we created at Scylla. It contains extensions to tokenAwareHostPolicy supported by the Scylla 2.3 and onwards. It allows driver to select a connection to a particular shard on a host based on the token. This eliminates passing data between shards and significantly reduces latency. The protocol extension spec is available here.

There are open pull requests to merge the functionality to the upstream project:

Installation

This is a drop-in replacement to gocql, to use it vendor as github.com/gocql/gocql.

With dep you can use source option:

[[constraint]]
  name = "github.com/gocql/gocql"
  source = "git@github.com:scylladb/gocql.git"
  branch = "master"

With glide you can use repo option:

- package: github.com/gocql/gocql
  vcs: git
  version: master
  repo: git@github.com:scylladb/gocql.git

With new Go modules you can use replace command:

go mod edit -replace=github.com/gocql/gocql=github.com/scylladb/gocql@{version}

where version is your intended version to be used. As gocql is currently not versioned you have to specify version in following format v0.0.0-%Y%m%d%H%M%S-{commit_sha:12}.
Full example:

go mod edit -replace=github.com/gocql/gocql=github.com/scylladb/gocql@v0.0.0-20181030092923-dc6f47ffd978

Configuration

In order to make shard-awareness work, token aware host selection policy has to be enabled. Please make sure that the gocql configuration has PoolConfig.HostSelectionPolicy properly set like in the example below.

When working with a Scylla cluster, PoolConfig.NumConns option has no effect - the driver opens one connection for each shard and completely ignores this option.

c := gocql.NewCluster(hosts...)

// Enable token aware host selection policy, if using multi-dc cluster set a local DC.
fallback := gocql.RoundRobinHostPolicy()
if localDC != "" {
	fallback = gocql.DCAwareRoundRobinPolicy(localDC)
}
c.PoolConfig.HostSelectionPolicy = gocql.TokenAwareHostPolicy(fallback)

// If using multi-dc cluster use the "local" consistency levels. 
if localDC != "" {
	c.Consistency = gocql.LocalQuorum
}

// When working with a Scylla cluster the driver always opens one connection per shard, so `NumConns` is ignored.
// c.NumConns = 4

Shard-aware port

This version of gocql supports a more robust method of establishing connection for each shard by using shard aware port for native transport. It greatly reduces time and the number of connections needed to establish a connection per shard in some cases - ex. when many clients connect at once, or when there are non-shard-aware clients connected to the same cluster.

If you are using a custom Dialer and if your nodes expose the shard-aware port, it is highly recommended to update it so that it uses a specific source port when connecting.

  • If you are using a custom net.Dialer, you can make your dialer honor the source port by wrapping it in a gocql.ScyllaShardAwareDialer:

    oldDialer := net.Dialer{...}
    clusterConfig.Dialer := &gocql.ScyllaShardAwareDialer{oldDialer}
  • If you are using a custom type implementing gocql.Dialer, you can get the source port by using the gocql.ScyllaGetSourcePort function. An example:

    func (d *myDialer) DialContext(ctx context.Context, network, addr string) (net.Conn, error) {
        sourcePort := gocql.ScyllaGetSourcePort(ctx)
        localAddr, err := net.ResolveTCPAddr(network, fmt.Sprintf(":%d", sourcePort))
        if err != nil {
            return nil, err
        }
        d := &net.Dialer{LocalAddr: localAddr}
        return d.DialContext(ctx, network, addr)
    }

    The source port might be already bound by another connection on your system. In such case, you should return an appropriate error so that the driver can retry with a different port suitable for the shard it tries to connect to.

    • If you are using net.Dialer.DialContext, this function will return an error in case the source port is unavailable, and you can just return that error from your custom Dialer.
    • Otherwise, if you detect that the source port is unavailable, you can either return gocql.ErrScyllaSourcePortAlreadyInUse or syscall.EADDRINUSE.

For this feature to work correctly, you need to make sure the following conditions are met:

  • Your cluster nodes are configured to listen on the shard-aware port (native_shard_aware_transport_port option),
  • Your cluster nodes are not behind a NAT which changes source ports,
  • If you have a custom Dialer, it connects from the correct source port (see the guide above).

The feature is designed to gracefully fall back to the using the non-shard-aware port when it detects that some of the above conditions are not met. The driver will print a warning about misconfigured address translation if it detects it. Issues with shard-aware port not being reachable are not reported in non-debug mode, because there is no way to detect it without false positives.

If you suspect that this feature is causing you problems, you can completely disable it by setting the ClusterConfig.DisableShardAwarePort flag to false.


Package gocql implements a fast and robust Cassandra client for the Go programming language.

Project Website: https://gocql.github.io/
API documentation: https://godoc.org/github.com/gocql/gocql
Discussions: https://groups.google.com/forum/#!forum/gocql

Supported Versions

The following matrix shows the versions of Go and Cassandra that are tested with the integration test suite as part of the CI build:

Go/Cassandra 2.1.x 2.2.x 3.x.x
1.15 yes yes yes
1.16 yes yes yes

Gocql has been tested in production against many different versions of Cassandra. Due to limits in our CI setup we only test against the latest 3 major releases, which coincide with the official support from the Apache project.

Sunsetting Model

In general, the gocql team will focus on supporting the current and previous versions of Go. gocql may still work with older versions of Go, but official support for these versions will have been sunset.

Installation

go get github.com/gocql/gocql

Features

  • Modern Cassandra client using the native transport
  • Automatic type conversions between Cassandra and Go
    • Support for all common types including sets, lists and maps
    • Custom types can implement a Marshaler and Unmarshaler interface
    • Strict type conversions without any loss of precision
    • Built-In support for UUIDs (version 1 and 4)
  • Support for logged, unlogged and counter batches
  • Cluster management
    • Automatic reconnect on connection failures with exponential falloff
    • Round robin distribution of queries to different hosts
    • Round robin distribution of queries to different connections on a host
    • Each connection can execute up to n concurrent queries (whereby n is the limit set by the protocol version the client chooses to use)
    • Optional automatic discovery of nodes
    • Policy based connection pool with token aware and round-robin policy implementations
  • Support for password authentication
  • Iteration over paged results with configurable page size
  • Support for TLS/SSL
  • Optional frame compression (using snappy)
  • Automatic query preparation
  • Support for query tracing
  • Support for Cassandra 2.1+ binary protocol version 3
    • Support for up to 32768 streams
    • Support for tuple types
    • Support for client side timestamps by default
    • Support for UDTs via a custom marshaller or struct tags
  • Support for Cassandra 3.0+ binary protocol version 4
  • An API to access the schema metadata of a given keyspace

Performance

While the driver strives to be highly performant, there are cases where it is difficult to test and verify. The driver is built with maintainability and code readability in mind first and then performance and features, as such every now and then performance may degrade, if this occurs please report and issue and it will be looked at and remedied. The only time the driver copies data from its read buffer is when it Unmarshal's data into supplied types.

Some tips for getting more performance from the driver:

  • Use the TokenAware policy
  • Use many goroutines when doing inserts, the driver is asynchronous but provides a synchronous API, it can execute many queries concurrently
  • Tune query page size
  • Reading data from the network to unmarshal will incur a large amount of allocations, this can adversely affect the garbage collector, tune GOGC
  • Close iterators after use to recycle byte buffers

Important Default Keyspace Changes

gocql no longer supports executing "use " statements to simplify the library. The user still has the ability to define the default keyspace for connections but now the keyspace can only be defined before a session is created. Queries can still access keyspaces by indicating the keyspace in the query:

SELECT * FROM example2.table;

Example of correct usage:

	cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
	cluster.Keyspace = "example"
	...
	session, err := cluster.CreateSession()

Example of incorrect usage:

	cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
	cluster.Keyspace = "example"
	...
	session, err := cluster.CreateSession()

	if err = session.Query("use example2").Exec(); err != nil {
		log.Fatal(err)
	}

This will result in an err being returned from the session.Query line as the user is trying to execute a "use" statement.

Example

See package documentation.

Data Binding

There are various ways to bind application level data structures to CQL statements:

  • You can write the data binding by hand, as outlined in the Tweet example. This provides you with the greatest flexibility, but it does mean that you need to keep your application code in sync with your Cassandra schema.
  • You can dynamically marshal an entire query result into an []map[string]interface{} using the SliceMap() API. This returns a slice of row maps keyed by CQL column names. This method requires no special interaction with the gocql API, but it does require your application to be able to deal with a key value view of your data.
  • As a refinement on the SliceMap() API you can also call MapScan() which returns map[string]interface{} instances in a row by row fashion.
  • The Bind() API provides a client app with a low level mechanism to introspect query meta data and extract appropriate field values from application level data structures.
  • The gocqlx package is an idiomatic extension to gocql that provides usability features. With gocqlx you can bind the query parameters from maps and structs, use named query parameters (:identifier) and scan the query results into structs and slices. It comes with a fluent and flexible CQL query builder that supports full CQL spec, including BATCH statements and custom functions.
  • Building on top of the gocql driver, cqlr adds the ability to auto-bind a CQL iterator to a struct or to bind a struct to an INSERT statement.
  • Another external project that layers on top of gocql is cqlc which generates gocql compliant code from your Cassandra schema so that you can write type safe CQL statements in Go with a natural query syntax.
  • gocassa is an external project that layers on top of gocql to provide convenient query building and data binding.
  • gocqltable provides an ORM-style convenience layer to make CRUD operations with gocql easier.

More Examples and Resources

The course Using Scylla Drivers in Scylla University explains how to use drivers in different languages to interact with a Scylla cluster. The lesson, Golang and Scylla Part 1 includes a sample application that, using the GoCQL driver, interacts with a three-node Scylla cluster. It connects to a Scylla cluster, displays the contents of a table, inserts and deletes data, and shows the contents of the table after each action.

Ecosystem

The following community maintained tools are known to integrate with gocql:

  • gocqlx is a gocql extension that automates data binding, adds named queries support, provides flexible query builders and plays well with gocql.
  • journey is a migration tool with Cassandra support.
  • negronicql is gocql middleware for Negroni.
  • cqlr adds the ability to auto-bind a CQL iterator to a struct or to bind a struct to an INSERT statement.
  • cqlc generates gocql compliant code from your Cassandra schema so that you can write type safe CQL statements in Go with a natural query syntax.
  • gocassa provides query building, adds data binding, and provides easy-to-use "recipe" tables for common query use-cases.
  • gocqltable is a wrapper around gocql that aims to simplify common operations.
  • gockle provides simple, mockable interfaces that wrap gocql types
  • scylladb is a fast Apache Cassandra-compatible NoSQL database
  • go-cql-driver is an CQL driver conforming to the built-in database/sql interface. It is good for simple use cases where the database/sql interface is wanted. The CQL driver is a wrapper around this project.

Other Projects

  • gocqldriver is the predecessor of gocql based on Go's database/sql package. This project isn't maintained anymore, because Cassandra wasn't a good fit for the traditional database/sql API. Use this package instead.

SEO

For some reason, when you Google golang cassandra, this project doesn't feature very highly in the result list. But if you Google go cassandra, then we're a bit higher up the list. So this is note to try to convince Google that golang is an alias for Go.

License

Copyright (c) 2012-2016 The gocql Authors. All rights reserved. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.

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Package gocql implements a fast and robust Cassandra client for the Go programming language.

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