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add the test suite for CockroachDB
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| Testing CockroachDB transaction isolation levels | ||
| =============================================== | ||
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| CockroachDB executes all transactions at the strongest transaction isolation level: **Serializable**. | ||
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| These tests were run with CockroachDB 20.2.3. | ||
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| Setup (before every test case): | ||
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| ```sql | ||
| create table test (id int primary key, value int); | ||
| insert into test (id, value) values (1, 10), (2, 20); | ||
| ``` | ||
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| Basic requirements (G0, G1a, G1b, G1c) | ||
| ----------------------------------------------------- | ||
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| CockroachDB "serializable" prevents Write Cycles (G0) by locking updated rows: | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| update test set value = 12 where id = 1; -- T2, BLOCKS | ||
| update test set value = 21 where id = 2; -- T1 | ||
| select * from test; -- T1. Shows 1 => 11, 2 => 21 | ||
| commit; -- T1. This unblocks T2 | ||
| update test set value = 22 where id = 2; -- T2 | ||
| commit; -- T2 | ||
| select * from test; -- either. Shows 1 => 12, 2 => 22 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Aborted Reads (G1a): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| update test set value = 101 where id = 1; -- T1 | ||
| select * from test; -- T2. Still shows 1 => 10 | ||
| abort; -- T1 | ||
| select * from test; -- T2. Still shows 1 => 10 | ||
| commit; -- T2 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Intermediate Reads (G1b): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| update test set value = 101 where id = 1; -- T1 | ||
| select * from test; -- T2. Still shows 1 => 10 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| commit; -- T1 | ||
| select * from test; -- T2. Still shows 1 => 10 | ||
| commit; -- T2 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Circular Information Flow (G1c): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| update test set value = 22 where id = 2; -- T2 | ||
| select * from test where id = 2; -- T1. Still shows 2 => 20 | ||
| select * from test where id = 1; -- T2. Still shows 1 => 10 | ||
| commit; -- T1 | ||
| commit; -- T2, ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_SERIALIZABLE - failed preemptive refresh) | ||
| ``` | ||
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| Observed Transaction Vanishes (OTV) | ||
| ----------------------------------- | ||
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| CockroachDB "serializable" prevents Observed Transaction Vanishes (OTV): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| begin; -- T3 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| update test set value = 19 where id = 2; -- T1 | ||
| update test set value = 12 where id = 1; -- T2. BLOCKS | ||
| commit; -- T1. This unblocks T2 | ||
| select * from test where id = 1; -- T3. Shows 1 => 10 | ||
| update test set value = 18 where id = 2; -- T2 | ||
| select * from test where id = 2; -- T3. Shows 2 => 20 | ||
| commit; -- T2 | ||
| select * from test where id = 2; -- T3. Shows 2 => 20 | ||
| select * from test where id = 1; -- T3. Shows 1 => 10 | ||
| commit; -- T3 | ||
| ``` | ||
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| Predicate-Many-Preceders (PMP) | ||
| ------------------------------ | ||
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| CockroachDB "serializable" prevents Predicate-Many-Preceders (PMP): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where value = 30; -- T1. Returns nothing | ||
| insert into test (id, value) values(3, 30); -- T2 | ||
| commit; -- T2 | ||
| select * from test where value % 3 = 0; -- T1. Still returns nothing | ||
| commit; -- T1 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Predicate-Many-Preceders (PMP) for write predicates -- example from Postgres documentation: | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| update test set value = value + 10 where true; -- T1 | ||
| delete from test where value = 20; -- T2, BLOCKS | ||
| commit; -- T1. T2 now prints out "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_WRITE_TOO_OLD - WriteTooOld flag converted to WriteTooOldError)" | ||
| abort; -- T2. There's nothing else we can do, this transaction has failed | ||
| ``` | ||
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| Lost Update (P4) | ||
| ---------------- | ||
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| CockroachDB "serializable" prevents Lost Update (P4): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where id = 1; -- T1 | ||
| select * from test where id = 1; -- T2 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| update test set value = 11 where id = 1; -- T2, BLOCKS | ||
| commit; -- T1. T2 now prints out "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: WriteTooOldError: write at timestamp 1609143635.427526584,0 too old; wrote at 1609143665.238193548,3" | ||
| abort; -- T2. There's nothing else we can do, this transaction has failed | ||
| ``` | ||
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| Read Skew (G-single) | ||
| -------------------- | ||
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| CockroachDB "serializable" prevents Read Skew (G-single): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where id = 1; -- T1. Shows 1 => 10 | ||
| select * from test where id = 1; -- T2 | ||
| select * from test where id = 2; -- T2 | ||
| update test set value = 12 where id = 1; -- T2 | ||
| update test set value = 18 where id = 2; -- T2 | ||
| commit; -- T2 | ||
| select * from test where id = 2; -- T1. Shows 2 => 20 | ||
| commit; -- T1 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Read Skew (G-single) -- test using predicate dependencies: | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where value % 5 = 0; -- T1 | ||
| update test set value = 12 where value = 10; -- T2 | ||
| commit; -- T2 | ||
| select * from test where value % 3 = 0; -- T1. Returns nothing | ||
| commit; -- T1 | ||
| ``` | ||
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| CockroachDB "serializable" prevents Read Skew (G-single) -- test using write predicate: | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin;-- T2 | ||
| select * from test where id = 1; -- T1. Shows 1 => 10 | ||
| select * from test; -- T2 | ||
| update test set value = 12 where id = 1; -- T2 | ||
| update test set value = 18 where id = 2; -- T2 | ||
| commit; -- T2 | ||
| delete from test where value = 20; -- T1. Prints "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_WRITE_TOO_OLD - WriteTooOld flag converted to WriteTooOldError)" | ||
| abort; -- T1. There's nothing else we can do, this transaction has failed | ||
| ``` | ||
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| Write Skew (G2-item) | ||
| -------------------- | ||
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| CockroachDB "serializable" prevents Write Skew (G2-item): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where id in (1,2); -- T1 | ||
| select * from test where id in (1,2); -- T2 | ||
| update test set value = 11 where id = 1; -- T1 | ||
| update test set value = 21 where id = 2; -- T2 | ||
| commit; -- T1 | ||
| commit; -- T2. Prints out "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_SERIALIZABLE - failed preemptive refresh)" | ||
| ``` | ||
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| Anti-Dependency Cycles (G2) | ||
| --------------------------- | ||
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| CockroachDB "serializable" prevents Anti-Dependency Cycles (G2): | ||
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| ```sql | ||
| begin; -- T1 | ||
| begin; -- T2 | ||
| select * from test where value % 3 = 0; -- T1 | ||
| select * from test where value % 3 = 0; -- T2 | ||
| insert into test (id, value) values(3, 30); -- T1 | ||
| insert into test (id, value) values(4, 42); -- T2 | ||
| commit; -- T1 | ||
| commit; -- T2. Prints out "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_SERIALIZABLE - failed preemptive refresh)" | ||
| ``` | ||
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| CockroachDB "serializable" prevents Anti-Dependency Cycles (G2) -- Fekete et al's example with two anti-dependency edges: | ||
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| ```sql | ||
| begin; -- T1 | ||
| select * from test; -- T1. Shows 1 => 10, 2 => 20 | ||
| begin; -- T2 | ||
| update test set value = value + 5 where id = 2; -- T2 | ||
| commit; -- T2 | ||
| begin; -- T3 | ||
| select * from test; -- T3. Shows 1 => 10, 2 => 25 | ||
| commit; -- T3 | ||
| update test set value = 0 where id = 1; -- T1. | ||
| commit; -- T1. Prints out "ERROR: restart transaction: TransactionRetryWithProtoRefreshError: TransactionRetryError: retry txn (RETRY_SERIALIZABLE - failed preemptive refresh)" | ||
| ``` |