test: Add test cases for arrays and objects, and introduce `verify_schema` #250

amotl · 2023-12-13T01:21:20Z

About

This patch just aims to improve the test cases by exercising a few more variants when using container types (array/object resp. list/dictionary).

Rationale

While PostgreSQL just uses the jsonb[] type for storing them, the details may be slightly different with other databases which are otherwise largely compatible with PostgreSQL. In particular, CrateDB uses dedicated ARRAY() and OBJECT() types for achieving the same thing what PostgreSQL does with JSON(B).

However, it is not exclusively about other databases, where target-postgres would not need to be concerned about. It is also about setting the stage for other ARRAY types, which may not be converged into JSONB, but into VECTOR(N) instead, when taking PostgreSQL database extensions into account, which provide other data types conceptionally matching built-in data types. In particular, with VECTOR(N), I am looking at pgvector here.

Details

In PostgreSQL, all boils down to the jsonb[] type, but arrays are reflected as sqlalchemy.dialects.postgresql.ARRAY instead of sqlalchemy.dialects.postgresql.JSONB. The new test cases both verify and outline that fact.

In order to prepare for more advanced type mangling & validation, and to better support databases pretending to be compatible with PostgreSQL, the new test cases exercise arrays with different kinds of inner values, because, on other databases, ARRAYs may need to have uniform content.

References

Along the lines, it adds a verify_schema utility function in the spirit of the verify_data function, refactored and generalized from the test_anyof test case, building upon the recent improvements by @sebastianswms.

feat: Verify data in tests (row count and first row) #215

target_postgres/tests/test_target_postgres.py

In PostgreSQL, all boils down to the `jsonb[]` type, but arrays are reflected as `sqlalchemy.dialects.postgresql.ARRAY` instead of `sqlalchemy.dialects.postgresql.JSONB`. In order to prepare for more advanced type mangling & validation, and to better support databases pretending to be compatible with PostgreSQL, the new test cases exercise arrays with different kinds of inner values, because, on other databases, ARRAYs may need to have uniform content. Along the lines, it adds a `verify_schema` utility function in the spirit of the `verify_data` function, refactored and generalized from the `test_anyof` test case.

visch · 2023-12-19T15:49:53Z

From first glance at this from the ticket you mentioned @amotl I wonder if just adding 5-10 more tests would trigger this or if it's specefic to how your test is written. I haven't dove into the code I'm just offering some ideas to help others. If just adding* 5-10 duplicate tests doesn't cause the issue, then there's something up with the specific test here and I'd look into https://github.com/MeltanoLabs/target-postgres/pull/250/files#diff-992edbd5794275b6bacd3fae33d85cc8dc11591daea563b2e65c8fa7b9b5bbf5R155 but that's a wild guess

amotl · 2023-12-19T18:10:18Z

@visch: Thank you for quickly looking into this.

I wonder if just adding 5-10 more tests would trigger this or if it's specefic to how your test is written. I haven't dove into the code I'm just offering some ideas to help others. If just adding* 5-10 duplicate tests doesn't cause the issue, then there's something up with the specific test here.

I think you are right on the spot, and your question sparked my motivation to also have a more closer look. By trying to make progress through trial-and-error, adding 8ec2a15 decreases the number of corresponding FATAL: sorry, too many clients already errors from 4 ¹ to 1 ².

Dispose the SQLAlchemy engine object after use within test utility functions.

Within `BasePostgresSDKTests`, new database connections via SQLAlchemy haven't been closed, and started filling up the connection pool, eventually saturating it.

Dispose the SQLAlchemy engine object after use within `PostgresConnector`.

amotl · 2023-12-19T20:45:47Z

By trying to make progress through trial-and-error...

Apparently, all of 8b3ea4f, a9d1796, 723e1fa are needed to remedy the flaw ¹. I am not sure if they are correct, but they resolve the problem at hand: The patch passes CI successfully now.

2eede7e was also tried, but didn't make a difference. ↩

amotl · 2023-12-19T22:11:57Z

target_postgres/connector.py

    @contextmanager
    def _connect(self) -> t.Iterator[sqlalchemy.engine.Connection]:
-        with self._engine.connect().execution_options() as conn:
+        engine = self._engine
+        with engine.connect().execution_options() as conn:
            yield conn
+        engine.dispose()


This spot relates to an issue we observed after adding more test cases. Other than any other related changes to the test suite, this one affects the connector implementation. Without that change, there seems to be a flaw which apparently qualifies as a resource leak, manifesting in connection pool overflow.

Tests are failing with FATAL: sorry, too many clients already #260

I would want to understand this fully before merging. What is the root cause of this problem? Are we confident that this is all that's required to close the leak?

Hi Sebastian. Thanks for your review. I can only say that this spot has been found out by educated guessing and a bit more trial-and-error, so it was kind of empirically determined, including the solution.

Apologies that I can't come up with a better reasoning/rationale, but I can offer to submit another repro PR without all the other changes here, in order to better demonstrate the issue.

sebastianswms · 2023-12-21T20:40:51Z

target_postgres/tests/test_target_postgres.py

+        "array_boolean",
+        check_columns={
+            "id": {"type": BIGINT},
+            "value": {"type": ARRAY},


Arrays have inner data types such as ARRAY[BOOLEAN] (not sure if that's the right syntax). We should additionally check for that.

I see your point. Let me check how verify_schema could be improved accordingly.

We are not looking at multiple dimensions here, or eventual nestedness, right? It would just be about »verifying the type of the first element within the array against its specification, when the array is not empty«, correct?

sebastianswms · 2023-12-21T20:42:08Z

target_postgres/connector.py

    @contextmanager
    def _connect(self) -> t.Iterator[sqlalchemy.engine.Connection]:
-        with self._engine.connect().execution_options() as conn:
+        engine = self._engine
+        with engine.connect().execution_options() as conn:
            yield conn
+        engine.dispose()


I would want to understand this fully before merging. What is the root cause of this problem? Are we confident that this is all that's required to close the leak?

amotl commented Dec 13, 2023

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target_postgres/tests/test_target_postgres.py Outdated Show resolved Hide resolved

amotl force-pushed the test-array-object branch from 55f98f4 to af77af4 Compare December 13, 2023 02:42

amotl force-pushed the test-array-object branch from af77af4 to e70dd58 Compare December 16, 2023 05:19

amotl added 2 commits December 19, 2023 16:16

chore: Add .idea to .gitignore

fe92e45

amotl force-pushed the test-array-object branch from e70dd58 to c0d4a89 Compare December 19, 2023 15:16

amotl changed the title ~~test: Add test cases for arrays and objects~~ test: Add test cases for arrays and objects, and introduce verify_schema Dec 19, 2023

amotl mentioned this pull request Dec 19, 2023

FATAL: sorry, too many clients already #124

Closed

visch mentioned this pull request Dec 19, 2023

Tests are failing with FATAL: sorry, too many clients already #260

Open

amotl force-pushed the test-array-object branch 2 times, most recently from 223a64c to e66085c Compare December 19, 2023 19:18

amotl added 2 commits December 19, 2023 21:26

test: Fix FATAL: sorry, too many clients already

8b3ea4f

Dispose the SQLAlchemy engine object after use within test utility functions.

test: Fix FATAL: sorry, too many clients already

a9d1796

Within `BasePostgresSDKTests`, new database connections via SQLAlchemy haven't been closed, and started filling up the connection pool, eventually saturating it.

amotl force-pushed the test-array-object branch 3 times, most recently from 5a70027 to 1722b80 Compare December 19, 2023 20:34

test: Fix FATAL: sorry, too many clients already

723e1fa

Dispose the SQLAlchemy engine object after use within `PostgresConnector`.

amotl force-pushed the test-array-object branch from 1722b80 to 723e1fa Compare December 19, 2023 20:41

amotl commented Dec 19, 2023

View reviewed changes

sebastianswms reviewed Dec 21, 2023

View reviewed changes

amotl mentioned this pull request Jan 18, 2024

chore: Harmonize imports of sqlalchemy module, use sa where applicable #255

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test: Add test cases for arrays and objects, and introduce `verify_schema` #250

test: Add test cases for arrays and objects, and introduce `verify_schema` #250

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test: Add test cases for arrays and objects, and introduce verify_schema #250

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test: Add test cases for arrays and objects, and introduce verify_schema #250

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amotl commented Dec 13, 2023 • edited Loading

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amotl commented Dec 19, 2023

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test: Add test cases for arrays and objects, and introduce `verify_schema` #250

test: Add test cases for arrays and objects, and introduce `verify_schema` #250

amotl commented Dec 13, 2023 •

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visch commented Dec 19, 2023 •

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