Transactions are applied on tablets without intents

[JDNdeveloper]

If you run the following SQL you will see two warning messages in the log.

SQL:

drop table if exists t;
create table t (k int primary key);
begin;
insert into t values (1);
select * from t where k = 2;
end;

Example warning messages:

W0814 18:31:58.293745 11289 transaction_participant.cc:1195] T 092c84b65a1d4cbaa44b7acc3a426e88 P 465bbc7ce57d438290cbc564c227c27a: Transaction not found: 3d5c46af-fa9c-4de5-a321-09d430ce6c9d, for: pre apply
W0814 18:31:58.293778 11289 transaction_participant.cc:1008] T 092c84b65a1d4cbaa44b7acc3a426e88 P 465bbc7ce57d438290cbc564c227c27a: Apply of unknown transaction: { transaction_id: 3d5c46af-fa9c-4de5-a321-09d430ce6c9d op_id: term: 1 index: 10062 commit_ht: { physical: 1565807518269905 logical: 16 } log_ht: { physical: 1565807518271659 logical: 3 } status_tablet: 5e697f9ed57046b4b9808d66d81fcc71 }

The warning message is caused by missing metadata on the tablet, which in turn is caused by the tablet never having intents written for the transaction. We should not be applying intents on tablets that do not actually contain intents for the given transaction.

In order to repro you simply need to perform a non-serializable read on a tablet that is not written to in the transaction. However, there is an optimization in the YB-PG client to not start a new distributed transaction until a write is actually performed, so you must first perform a write, and then you can perform the read on a different tablet which will repro the issue. We do not have this problem with serializable reads as they write read intents, so apply/cleanup should still be performed on these tablets.

Fixing this issue by not applying intents on these tablets will get rid of the warning message, but will also have the benefit of avoiding extraneous RPCs and minimizing the number of tablets the transaction coordinator (i.e. status tablet) has to wait for in both Apply and Cleanup.