Does Cassandra Insert JSON creates Tombstones?

问题

I am using Cassandra's insert JSON feature to insert data into the table. In the JSON that I create, I do not include the null values. Meaning, ignore the fields that have null values in it.

Does Cassandra create tombstones in such cases, if I am inserting the record say, for the first time?

I assume for subsequent upsert for the same key will create tombstone. Is that right?

回答1:

Cell tombstone should still get created for the values which are not included in the json you are trying to insert.

Consider a table called cyclist having id, first name and last name. We will insert a row using a json string which contains only last name.

CREATE KEYSPACE IF NOT EXISTS cycling WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'datacenter1' : 3 };

CREATE TABLE cycling.cyclist ( id UUID PRIMARY KEY, first_name text, last_name text );

CREATE TABLE cycling.cyclist ( id UUID PRIMARY KEY, first_name text, last_name text );

INSERT INTO cycling.cyclist JSON '{"id" : "829aa84a-4bba-411f-a4fb-38167a987cda", "last_name" : "MYLASTNAME" }';

Now if we look at the data structure within sstable, it looks like below.

[
  {
    "partition" : {
      "key" : [ "829aa84a-4bba-411f-a4fb-38167a987cda" ],
      "position" : 0
    },
    "rows" : [
      {
        "type" : "row",
        "position" : 30,
        "liveness_info" : { "tstamp" : "2020-05-13T07:10:59.298374Z" },
        "cells" : [
          { "name" : "first_name", "deletion_info" : { "local_delete_time" : "2020-05-13T07:10:59Z" }
          },
          { "name" : "last_name", "value" : "MYLASTNAME" }
        ]
      }
    ]
  }
]

Observe the cell tombstone created for first_name.

This is different than the sstable structure when we insert the data using selective fields.

INSERT INTO cycling.cyclist(id, first_name) VALUES ( 'c49d1614-e841-4bd4-993b-02d49ae7414c', 'MYFIRSTNAME');

Now look at the sstable structure

[
  {
    "partition" : {
      "key" : [ "829aa84a-4bba-411f-a4fb-38167a987cda" ],
      "position" : 0
    },
    "rows" : [
      {
        "type" : "row",
        "position" : 30,
        "liveness_info" : { "tstamp" : "2020-05-13T07:10:59.298374Z" },
        "cells" : [
          { "name" : "first_name", "deletion_info" : { "local_delete_time" : "2020-05-13T07:10:59Z" }
          },
          { "name" : "last_name", "value" : "MYLASTNAME" }
        ]
      }
    ]
  },
  {
    "partition" : {
      "key" : [ "c49d1614-e841-4bd4-993b-02d49ae7414c" ],
      "position" : 47
    },
    "rows" : [
      {
        "type" : "row",
        "position" : 77,
        "liveness_info" : { "tstamp" : "2020-05-13T07:23:42.964609Z" },
        "cells" : [
          { "name" : "first_name", "value" : "MYFIRSTNAME" }
        ]
      }
    ]
  }
]

来源：https://stackoverflow.com/questions/61768228/does-cassandra-insert-json-creates-tombstones

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cassandra

tombstone