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new 09a455a1 Fix flaky largecolumn_test.TestLargeColumn: force GC before
direct memory measurements for ZGC compatibility
09a455a1 is described below
commit 09a455a1c5267951db1954559209bcbe3a5416b3
Author: samlightfoot <[email protected]>
AuthorDate: Sat Feb 21 11:50:32 2026 +0000
Fix flaky largecolumn_test.TestLargeColumn: force GC before direct memory
measurements for ZGC compatibility
Generational ZGC (JDK 21 default) only processes PhantomReferences
during major collections, which may not trigger during short test runs.
This causes DirectByteBuffer Cleaners to not fire, leaving ~63MB of
stale direct memory that inflates TOTAL_CAPACITY and fails the assertion.
Force System.gc() via nodetool is addedbefore each measurement to ensure a
major
collection runs and reference processing completes.
patch by Sam Lightfoot; reviewed by Dmitry Konstantinov, Brandon Williams
for CASSANDRA-21182
---
largecolumn_test.py | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/largecolumn_test.py b/largecolumn_test.py
index d7d4a696..9bd1d228 100644
--- a/largecolumn_test.py
+++ b/largecolumn_test.py
@@ -1,6 +1,8 @@
import pytest
import re
import logging
+import subprocess
+import time
from dtest import Tester
@@ -69,16 +71,28 @@ class TestLargeColumn(Tester):
# Now run the full stack to warm up internal caches/pools
LARGE_COLUMN_SIZE = 1024 * 1024 * 63
self.stress_with_col_size(cluster, node1, LARGE_COLUMN_SIZE)
- after1stLargeStress = self.directbytes(node1)
+ after1stLargeStress = self.directbytes_post_gc(node1)
logger.info("After 1st large column stress, direct memory:
{0}".format(after1stLargeStress))
# Now run the full stack to see how much memory is allocated for the
second "large" columns request
self.stress_with_col_size(cluster, node1, LARGE_COLUMN_SIZE)
- after2ndLargeStress = self.directbytes(node1)
+ after2ndLargeStress = self.directbytes_post_gc(node1)
logger.info("After 2nd large column stress, direct memory:
{0}".format(after2ndLargeStress))
# We may allocate direct memory proportional to size of a request
# but we want to ensure that when we do subsequent calls the used
direct memory is not growing
- diff = int(after2ndLargeStress) - int(after1stLargeStress)
+ diff = after2ndLargeStress - after1stLargeStress
logger.info("Direct memory delta: {0}".format(diff))
assert diff < LARGE_COLUMN_SIZE
+
+ def directbytes_post_gc(self, node):
+ """Trigger GC and wait for the Cleaner thread to release
DirectByteBuffers.
+
+ Generational ZGC (JDK 21) only processes PhantomReferences during major
+ collections which may not run during short tests. After GC, the Cleaner
+ daemon thread decrements TOTAL_CAPACITY asynchronously, so we sleep to
+ allow it to complete.
+ """
+ subprocess.check_call(['jcmd', str(node.pid), 'GC.run'])
+ time.sleep(3)
+ return int(self.directbytes(node))
\ No newline at end of file
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