Redis

The redis asynchronous driver provides an interface to work with Redis standalone instances, as well as Redis Sentinels and Clusters.

Take note that Redis is not able to guarantee a strong consistency. It is possible for Redis to lose writes that were acknowledged, and vice versa.

Main features

• Convenient methods for Redis commands returning proper C++ types;
• Support for bulk operations (MGET, MSET, etc); driver splits data into smaller chunks if necessary to increase server responsiveness;
• Support for different strategies of choosing the most suitable Redis instance;
• Request timeouts management with transparent retries.

Metrics

Metric name	Description
redis.instances_count	current number of Redis instances
redis.last_ping_ms	last measured ping value
redis.is_ready	1 if connected and ready, 0 otherwise
redis.not_ready_ms	milliseconds since last ready status
redis.reconnects	reconnect counter
redis.session-time-ms	milliseconds since connected to instance
redis.timings	query timings
redis.errors	counter of failed requests

See Service Statistics and Metrics (Prometheus/Graphite/...) for info on how to get the metrics.

Usage

To use Redis you must add the component components::Redis and configure it according to the documentation. After that you can make requests via storages::redis::Client:

void RedisClientSampleUsage(storages::redis::Client& client) {
  client.Rpush("sample_list", "a", {}).Get();
  client.Rpush("sample_list", "b", {}).Get();
  const auto length = client.Llen("sample_list", {}).Get();
 
  EXPECT_EQ(length, 2);
}

Timeouts

Request timeout can be set for a single request via redis::CommandControl argument.

Dynamic option REDIS_DEFAULT_COMMAND_CONTROL can be used to set default values.

To interrupt a request on the client side, you can use cancellation mechanism to cancel the task that executes the Redis request:

std::optional<std::string> RedisClientCancelRequest(
    storages::redis::Client& client) {
  auto result = client.Get("foo", {});
 
  engine::current_task::GetCancellationToken().RequestCancel();
 
  // Throws redis::RequestCancelledException if Redis was not
  // fast enough to answer
  return result.Get();
}

Redis driver does not guarantee that the cancelled request was not executed by the server.

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