Document the glibc static-TLS ImportError in the FAQ - #801
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Add an entry for 'cannot allocate memory in static TLS block', a recurring ImportError when other native extensions have already claimed glibc's small static-TLS surplus before _mysql dlopen()s. It has hit multiple unrelated consumers (Apache Airflow #17546 and its 2024 recurrence in #40503) but was never documented here. Signed-off-by: 1fanwang <1fannnw@gmail.com>
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Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe FAQ explains the static-TLS ChangesStatic TLS FAQ
Priority: ⬇️ Low Estimated code review effort: 1 (Trivial) | ~2 minutes Change: Other Merge Risk: ⚪ Minimal · up to The static-TLS workaround documentation includes its process scope and potential performance costs, with no remaining actionable merge risk. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@doc/FAQ.rst`:
- Around line 105-108: Update the LD_PRELOAD workaround documentation in the FAQ
to state that the exported variable affects child processes in the service or
container. Also document that preloading libstdc++.so.6 adds hundreds of
milliseconds to startup and a small memory overhead for binaries that do not
already link it.
- Line 112: Update the LD_PRELOAD example to derive the library directory from
the platform’s Debian multiarch name using dpkg-architecture
-qDEB_HOST_MULTIARCH or gcc -print-multiarch, replacing the uname -m-based path
while preserving the existing libstdc++.so.6 target.
- Around line 94-98: Revise the FAQ explanation to state that previously loaded
native extensions can consume glibc’s static-TLS surplus, particularly through
their TLS allocation models, before the dynamic loader loads MySQLdb._mysql or
one of its dependencies. Remove the implication that each extension separately
links libstdc++ or that _mysql calls dlopen(), while preserving the distinction
from a MySQLdb build bug.
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doc/FAQ.rst
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Signed-off-by: 1fanwang <1fannnw@gmail.com>
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Why are you creating this PR now? Have you encountered this issue recently? If so, could you provide more details, such as your OS and the versions of Python and the relevant libraries? |
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ChatGPT identified the root cause of this issue. It has already been reported on bugs.mysql.com. If you have encountered this issue, please click “Affects Me” on the bug report. |
2 participants
Why
Importing
MySQLdbcan fail after other native modules consume glibc's static-TLS space, even when mysqlclient was built correctly:What
The FAQ explains the loader failure and a process-scoped preload workaround. The Debian example obtains its library directory from the multiarch name rather than assuming it matches the kernel architecture name. Export inheritance and workload-dependent costs are explicit.
Refs
Testing
Executed in a Debian amd64 container with Python 3.12, mysqlclient, dpkg-dev and Sphinx installed, from the documentation directory:
Commands and raw output
These runs exercise the example and HTML rendering, not TLS exhaustion. The missing static-directory warning comes from the unchanged documentation configuration.
Summary by CodeRabbit
ImportErrorissues, including clearer explanations of causes and limitations.LD_PRELOADworkaround to determine the library path more reliably.