| Measurement |
Description |
Measurement Unit |
Interpretation |
| Client_id |
Indicates the client ID |
|
|
| IP_address |
Reports the IP address of this client. |
|
|
| Port_number |
Indicates the port at which this client listens. |
Number |
|
| Socket_dis_entry |
Reports the socket file descriptor number of this client. |
Number |
|
| DataBase_id |
Indicates the current database ID of this client. |
Number |
|
| Age |
Indicates the total duration of this client's connection. |
Seconds |
|
| Idle_time |
Indicates the duration for which this client's connection was idle. |
Seconds |
By default recent versions of Redis don't close the connection with the client if the client is idle for many seconds: the connection will remain open forever
However, there are two conditions when it makes sense to set a timeout:
Mission critical applications where a bug in the client software may saturate the Redis server with idle connections, causing service disruption. As a debugging mechanism in order to be able to connect with the server if a bug in the client software saturates the server with idle connections, making it impossible to interact with the server.
You can configure a timeout value via redis.conf or simply using CONFIG SET timeout <value>. |
| Channel_subscriptions |
Indicates the number of channels to which this client subscribes. |
Number |
Redis Pub/Sub implements the (in redis terminology called publishers) sends the messages while the receivers (subscribers) receive them. The link by which the messages are transferred is called channel. In Redis, a client can subscribe any number of channels. |
| Pattern_subscriptions |
Indicates the number of glob-style patterns this client subscribes to. |
Number |
The Redis Pub/Sub implementation supports pattern matching. Clients may subscribe to glob-style patterns in order to receive all the messages sent to channel names matching a given pattern. |
| Query_buffer_length |
Indicates the length of the query buffer (in MB) of this client. |
MB |
If this measure reports the value 0, it means no queries are pending.
Ideally, the value of this measure should be low. A high value or a consistent increase in this value could indicate the queries from the client are not being processed fast enough by the server.
If the value of this measure reaches the hard limit of 1 GB, the client connection may close automatically. This is done to avoid a server crash in case of client or server software bugs. |
| Query_buffer_free |
Indicates the amount of free space in the query buffer of this client. |
MB |
If this measure reports the value 0, it means that there is no free space in the query buffer. In this case, the client connection may close automatically. This is done to avoid a server crash in case of client or server software bugs.
Ideally, a high value is desired for this measure. A steady drop in the value of this measure could imply that the query buffer is rapidly filling up. This could be because of a probable query processing bottleneck on the server. |
| Output_buffer_length |
Indicates the length (in MB) of the output buffer of this client. |
MB |
Redis needs to handle a variable-length output buffer for every client, since a command can produce a big amount of data that needs to be transferred to the client. |
| Output_list_length |
Indicates the number of responses enqueued in the output list of this client. |
Number |
If the output buffer is not correctly sized, then it can fill up quickly, causing subsequent responses to clients to be enqueued in an output list. If the value of this measure is abnormally high for a client, it means that the output list is very long; this in turn is a sign that the output buffer needs resizing |
| Output_buffer_memory |
Indicates the amount of output buffer memory used up by the responses to this client. |
MB |
Sometimes, a client may send more commands producing more output to serve at a faster rate at which Redis can send the existing output to the client. This is especially true with Pub/Sub clients in case a client is not able to process new messages fast enough.
Both the conditions will cause the client output buffer to grow and consume more and more memory. In such a cases, this measure will report an abnormally high value.
To limit the usage of output buffer memory, by default, Redis sets limits to the output buffer size for different kind of clients. When the limit is reached the client connection is closed and the event logged in the Redis log file.
There are two kind of limits Redis uses:
The hard limit is a fixed limit that when reached will make Redis closing the client connection as soon as possible. The soft limit instead is a limit that depends on the time, for instance a soft limit of 32 megabytes per 10 seconds means that if the client has an output buffer bigger than 32 megabytes for, continuously, 10 seconds, the connection gets closed.
Different kind of clients have different default limits:
Normal clients have a default limit of 0, that means, no limit at all, because most normal clients use blocking implementations sending a single command and waiting for the reply to be completely read before sending the next command, so it is always not desirable to close the connection in case of a normal client. Pub/Sub clients have a default hard limit of 32 megabytes and a soft limit of 8 megabytes per 60 seconds. Slaves have a default hard limit of megabyte per 60 second.
It is possible to change the limit at runtime using the CONFIG SET command or in a permanent way using the Redis configuration file redis.conf. |