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TTL

TTL indicates time to live. Use the TTL options to specify a timeout for a property. Once timed out, the property expires.

OpenCypher Compatibility

This topic applies to nGQL extensions only.

Precautions

  • You CANNOT modify a property with TTL options on it.
  • TTL options and indexes CANNOT coexist on a tag or an edge type. Not even if you try to set them on different properties.

Data expiration and deletion

Vertex property expiration

Vertex property expiration has the following impact.

  • If a vertex has only one tag, once a property of the vertex expires, the vertex expires.
  • If a vertex has multiple tags, once a property of the vertex expires, properties bound to the same tag with the expired property also expires, but the vertex does not expire and other properties of it remain untouched.

Edge property expiration

Since an edge can have only one edge type, once an edge property expires, the edge expires.

Data deletion

The expired data are still stored on the disk, but queries will filter them out.

Nebula Graph automatically deletes the expired data and reclaims the disk space during the next compaction.

Note

If TTL is disabled, the corresponding data deleted after the last compaction can be queried again.

TTL options

The nGQL TTL feature has the following options.

Option Description
ttl_col Specifies the property to set a timeout on. The data type of the property must be int or timestamp.
ttl_duration Specifies the timeout adds-on value in seconds. The value must be a non-negative int64 number. A property expires if the sum of its value and the ttl_duration value is smaller than the current timestamp. If the ttl_duration value is 0, the property never expires.

Use TTL options

You must use the TTL options together to set a valid timeout on a property.

Set a timeout if a tag or an edge type exists

If a tag or an edge type is already created, to set a timeout on a property bound to the tag or edge type, use ALTER to update the tag or edge type.

// Create a tag.
nebula> CREATE TAG t1 (a timestamp);
Execution succeeded (time spent 4172/5377 us)

// Use ALTER to update the tag and set the TTL options.
nebula> ALTER TAG t1 ttl_col = "a", ttl_duration = 5;
Execution succeeded (time spent 2975/3700 us)

// Insert a vertex with tag t1. The vertex expires 5 seconds after the insertion.
nebula> INSERT VERTEX t1(a) values "101":(now());
Execution succeeded (time spent 1902/2642 us)

Set a timeout when creating a tag or an edge type

Use TTL options in the CREATE statement to set a timeout when creating a tag or an edge type. For more information, see CREATE TAG or CREATE EDGE.

// Create a tag and set the TTL options.
nebula> CREATE TAG t2(a int, b int, c string) ttl_duration= 100, ttl_col = "a";
Execution succeeded (time spent 3173/3753 us)

// Insert a vertex with tag t2.
// The timeout timestamp is 1612778164774 (1612778164674 + 100).
nebula> INSERT VERTEX t2(a, b, c) values "102":(1612778164674, 30, "Hello");
Execution succeeded (time spent 1254/1921 us)

Remove a timeout

To disable TTL and remove the timeout on a property, use the following approaches.

  • Set ttl_col to an empty string.
    nebula> ALTER TAG t1 ttl_col = "";
    
  • Drop the property with the timeout.
    nebula> ALTER TAG t1 DROP (a);
    
  • Set ttl_duration to 0. This operation keeps the TTL options and prevents the property from expiring.

    nebula> ALTER TAG t1 ttl_duration = 0;
    

    Caution

    Even when ttl_duration is 0, you CANNOT alter the property because it still has TTL options.


Last update: April 22, 2021