Document how null values are managed

[stevebang]

Jira Link: DB-1910
Document:

• how sparse datasets are managed
• NULL values are not stored
• subtlety about handling rows where most columns are NULL
• hidden system column that indicates row existence

See:

• @mbautin answer: https://forum.yugabyte.com/t/how-does-yugabyte-db-store-null-values-internally/318/2
• https://docs.yugabyte.com/latest/architecture/docdb/persistence/

[stevebang]

See also this thread in Slack (yugabyte-db) on Aug. 22, 2019:

James Hartig Today at 7:06 AM
Are NULL values just like cassandra, where if I don't include the field in the INSERT it's not stored at all but if I actually send a NULL then it stores a tombstone? Any downsides to not having the field stored at all?

2 replies

Kannan Muthukkaruppan 3 hours ago
@james Hartig - that is correct. It is more efficient to not send those NULLs since they will not be stored at all. And no downsides to it.

James Hartig 3 hours ago
👍 thanks

[stevebang]

Another source of info for what might be relevant to discuss: https://www.sqlite.org/nulls.html