# Message retention and expiry

Pulsar brokers are responsible for handling messages that pass through Pulsar, including persistent storage of messages. By default, brokers:

• immediately delete all messages that have been acknowledged on every subscription, and
• persistently store all unacknowledged messages in a backlog.

In Pulsar, you can override both of these default behaviors, at the namespace level, in two ways:

• You can persistently store messages that have already been consumed and acknowledged for a minimum time by setting retention policies.
• Messages that are not acknowledged within a specified timeframe, can be automatically marked as consumed, by specifying the time to live (TTL).

Pulsar's admin interface enables you to manage both retention policies and TTL at the namespace level (and thus within a specific tenant and either on a specific cluster or in the global cluster).

#### Retention and TTL are solving two different problems​

• Message retention: Keep the data for at least X hours (even if acknowledged)
• Time-to-live: Discard data after some time (by automatically acknowledging)

In most cases, applications will want to use either one or the other (or none).

## Retention policies​

By default, when a Pulsar message arrives at a broker it will be stored until it has been acknowledged by a consumer, at which point it will be deleted. You can override this behavior and retain even messages that have already been acknowledged by setting a retention policy on all the topics in a given namespace. When you set a retention policy you can set either a size limit or a time limit.

When you set a size limit of, say, 10 gigabytes, then messages in all topics in the namespace, even acknowledged messages, will be retained until the size limit for the topic is reached; if you set a time limit of, say, 1 day, then messages for all topics in the namespace will be retained for 24 hours.

It is also possible to set infinite retention time or size, by setting -1 for either time or size retention.

### Defaults​

There are two configuration parameters that you can use to set instance-wide defaults for message retention: defaultRetentionTimeInMinutes=0 and defaultRetentionSizeInMB=0.

Both of these parameters are in the broker.conf configuration file.

### Set retention policy​

You can set a retention policy for a namespace by specifying the namespace as well as both a size limit and a time limit.

Use the set-retention subcommand and specify a namespace, a size limit using the -s/--size flag, and a time limit using the -t/--time flag.

##### Examples​

To set a size limit of 10 gigabytes and a time limit of 3 hours for the my-tenant/my-ns namespace:

$pulsar-admin namespaces set-retention my-tenant/my-ns \ --size 10G \ --time 3h To set retention with infinite time and a size limit: $ pulsar-admin namespaces set-retention my-tenant/my-ns \  --size 1T \  --time -1

Similarly, even the size can be to unlimited:

#### Java​

admin.namespaces().getRetention(namespace);

## Backlog quotas​

Backlogs are sets of unacknowledged messages for a topic that have been stored by bookies. Pulsar stores all unacknowledged messages in backlogs until they are processed and acknowledged.

You can control the allowable size of backlogs, at the namespace level, using backlog quotas. Setting a backlog quota involves setting:

• an allowable size threshold for each topic in the namespace
• a retention policy that determines which action the broker takes if the threshold is exceeded.

The following retention policies are available:

PolicyAction
producer_request_holdThe broker will hold and not persist produce request payload
producer_exceptionThe broker will disconnect from the client by throwing an exception
consumer_backlog_evictionThe broker will begin discarding backlog messages

#### Beware the distinction between retention policy types​

As you may have noticed, there are two definitions of the term "retention policy" in Pulsar, one that applies to persistent storage of already-acknowledged messages and one that applies to backlogs.

Backlog quotas are handled at the namespace level. They can be managed via:

### Set size thresholds and backlog retention policies​

You can set a size threshold and backlog retention policy for all of the topics in a namespace by specifying the namespace, a size limit, and a policy by name.

Use the set-backlog-quota subcommand and specify a namespace, a size limit using the -l/--limit flag, and a retention policy using the -p/--policy flag.

#### Java​

Map<BacklogQuota.BacklogQuotaType,BacklogQuota> quotas =  admin.namespaces().getBacklogQuotas(namespace);

### Remove backlog quotas​

Use the remove-backlog-quota subcommand and specify a namespace. Here's an example:

$pulsar-admin namespaces remove-backlog-quota my-tenant/my-ns #### REST API​ DELETE /admin/v2/namespaces/:tenant/:namespace/backlogQuota #### Java​ admin.namespaces().removeBacklogQuota(namespace); ### Clear backlog​ #### pulsar-admin​ Use the clear-backlog subcommand. ##### Example​ $ pulsar-admin namespaces clear-backlog my-tenant/my-ns

By default, you will be prompted to ensure that you really want to clear the backlog for the namespace. You can override the prompt using the -f/--force flag.

## Time to live (TTL)​

By default, Pulsar stores all unacknowledged messages forever. This can lead to heavy disk space usage in cases where a lot of messages are going unacknowledged. If disk space is a concern, you can set a time to live (TTL) that determines how long unacknowledged messages will be retained.

### Set the TTL for a namespace​

Use the set-message-ttl subcommand and specify a namespace and a TTL (in seconds) using the -ttl/--messageTTL flag.
$pulsar-admin namespaces set-message-ttl my-tenant/my-ns \ --messageTTL 120 # TTL of 2 minutes #### REST API​ POST /admin/v2/namespaces/:tenant/:namespace/messageTTL #### Java​ admin.namespaces().setNamespaceMessageTTL(namespace, ttlInSeconds); ### Get the TTL configuration for a namespace​ #### pulsar-admin​ Use the get-message-ttl subcommand and specify a namespace. ##### Example​ $ pulsar-admin namespaces get-message-ttl my-tenant/my-ns60
admin.namespaces().getNamespaceMessageTTL(namespace)