java
9 minJava equals and hashCode: Fix Broken HashMap and HashSet Lookups
Diagnose collection bugs caused by inconsistent equality, mutable keys, inheritance, and accidental identity comparisons.
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databases
10 minFix Slow SQL: N+1 Queries, Missing Indexes, and Bad Cardinality Estimates
A systematic approach to diagnosing ORM query explosions and slow database plans without guessing at indexes.
Q&A
Q&AHow do you detect and fix a Java deadlock?
Find a cycle in lock ownership and waiting, then remove inconsistent nested lock ordering.
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Capture repeated thread dumps with jcmd or jstack while the incident is active. A deadlock cycle shows threads waiting for locks held by each other; distinguish it from starvation or a slow dependency by checking whether owners can progress. Fix consistent lock order, shorten critical sections, or redesign ownership so both locks are not required together.
java
10 minJava Exception Debugging: Trace the Root Cause and Fix the Boundary
A practical method for investigating wrapped exceptions, null failures, resource exhaustion, and misleading catch blocks in JVM services.
Q&A
Q&AWhy does a byte offset alone not make a download safe to resume?
The representation may have changed since the saved prefix was downloaded.
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Use a validator such as a strong ETag with If-Range, validate the 206 Content-Range before append, and verify final integrity separately. An ETag is not necessarily a cryptographic digest.
Q&A
Q&AHow do you confirm and fix an ORM N+1 query?
Count repeated statements per request, then batch-load without changing result cardinality.
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Trace or log normalized SQL for one request and look for the same child lookup repeated once per parent row. Replace the loop with an eager/batch load or a query at the correct grain. Verify query count and returned rows; a broad join can fix round trips while accidentally multiplying results.
python
9 minPython Error Debugging: Tracebacks, Root Causes, and Safe Fixes
Turn Python exceptions into a reproducible diagnosis using traceback frames, minimal experiments, structured logging, and boundary validation.
Q&A
Q&AHow do you fix a Python TypeError caused by None?
Trace why a value is absent and validate or model optionality where it enters the system.
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Find the first operation that received None and trace the producer branch, database field, or external payload that supplied it. Decide whether absence is valid: represent it as Optional and handle it explicitly, or reject malformed input at the boundary. Blindly substituting an empty string or zero can hide an invalid state and change business meaning.