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092a9b74d3
Newer version of mypy fixes buggy error when trying to update only boto3 stubs. However it brings new checks and starts to yell when we index into cusror.fetchone without checking for None first. So this introduces a wrapper to simplify quering for scalar values. I tried to use cursor_factory connection argument but without success. There can be a better way to do that, but this looks the simplest
71 lines
3.0 KiB
Python
71 lines
3.0 KiB
Python
from fixtures.neon_fixtures import NeonEnvBuilder
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from fixtures.log_helper import log
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from fixtures.utils import print_gc_result, query_scalar
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import psycopg2.extras
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#
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# Test where Postgres generates a lot of WAL, and it's garbage collected away, but
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# no pages are evicted so that Postgres uses an old LSN in a GetPage request.
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# We had a bug where the page server failed to find the page version because it
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# thought it was already garbage collected away, because the LSN in the GetPage
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# request was very old and the WAL from that time was indeed already removed.
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# In reality, the LSN on a GetPage request coming from a primary server is
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# just a hint that the page hasn't been modified since that LSN, and the page
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# server should return the latest page version regardless of the LSN.
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#
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def test_old_request_lsn(neon_env_builder: NeonEnvBuilder):
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# Disable pitr, because here we want to test branch creation after GC
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neon_env_builder.pageserver_config_override = "tenant_config={pitr_interval = '0 sec'}"
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env = neon_env_builder.init_start()
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env.neon_cli.create_branch("test_old_request_lsn", "main")
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pg = env.postgres.create_start('test_old_request_lsn')
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log.info('postgres is running on test_old_request_lsn branch')
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pg_conn = pg.connect()
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cur = pg_conn.cursor()
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# Get the timeline ID of our branch. We need it for the 'do_gc' command
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timeline = query_scalar(cur, "SHOW neon.timeline_id")
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psconn = env.pageserver.connect()
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pscur = psconn.cursor(cursor_factory=psycopg2.extras.DictCursor)
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# Create table, and insert some rows. Make it big enough that it doesn't fit in
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# shared_buffers.
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cur.execute('CREATE TABLE foo (id int4 PRIMARY KEY, val int, t text)')
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cur.execute('''
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INSERT INTO foo
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SELECT g, 1, 'long string to consume some space' || g
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FROM generate_series(1, 100000) g
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''')
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# Verify that the table is larger than shared_buffers, so that the SELECT below
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# will cause GetPage requests.
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cur.execute('''
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select setting::int * pg_size_bytes(unit) as shared_buffers, pg_relation_size('foo') as tbl_ize
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from pg_settings where name = 'shared_buffers'
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''')
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row = cur.fetchone()
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assert row is not None
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log.info(f'shared_buffers is {row[0]}, table size {row[1]}')
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assert int(row[0]) < int(row[1])
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cur.execute('VACUUM foo')
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# Make a lot of updates on a single row, generating a lot of WAL. Trigger
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# garbage collections so that the page server will remove old page versions.
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for i in range(10):
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pscur.execute(f"do_gc {env.initial_tenant.hex} {timeline} 0")
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row = pscur.fetchone()
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print_gc_result(row)
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for j in range(100):
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cur.execute('UPDATE foo SET val = val + 1 WHERE id = 1;')
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# All (or at least most of) the updates should've been on the same page, so
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# that we haven't had to evict any dirty pages for a long time. Now run
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# a query that sends GetPage@LSN requests with the old LSN.
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cur.execute("SELECT COUNT(*), SUM(val) FROM foo")
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assert cur.fetchone() == (100000, 101000)
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