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TTL

TTL (Time To Live) specifies a timeout for a property. Once timed out, the property expires.

OpenCypher Compatibility

This topic applies to native nGQL only.

Precautions

  • You CANNOT modify a property schema with TTL options on it.
  • TTL options and indexes have coexistence issues.

    • TTL options and indexes CANNOT coexist on a tag or an edge type. If there is an index on a property, you cannot set TTL options on other properties.
    • If there are TTL options on a tag, an edge type, or a property, you can still add an index on them.

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 expire, 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.

NebulaGraph 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 native 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.

Note

When the TTL options are set for a property and the property's value is NULL, 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 IF NOT EXISTS t1 (a timestamp);

# Use ALTER to update the tag and set the TTL options.
nebula> ALTER TAG t1 TTL_COL = "a", TTL_DURATION = 5;

# Insert a vertex with tag t1. The vertex expires 5 seconds after the insertion.
nebula> INSERT VERTEX t1(a) VALUES "101":(now());

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 and CREATE EDGE.

# Create a tag and set the TTL options.
nebula> CREATE TAG IF NOT EXISTS t2(a int, b int, c string) TTL_DURATION= 100, TTL_COL = "a";

# Insert a vertex with tag t2. The timeout timestamp is 1648197238 (1648197138 + 100).
nebula> INSERT VERTEX t2(a, b, c) VALUES "102":(1648197138, 30, "Hello");

Remove a timeout

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

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

Last update: December 6, 2022