Hidden Assumptions in redis
12 assumptions this code never checks · 4 critical · spanning Resource, Temporal, Contract, Shape, Domain, Scale, Environment, Ordering
Every codebase relies on things it never checks. Most of them are routine. CodeSea looked at redis/redis and picked out the few most likely to cause trouble. The full list is just below.
Most of what this code assumes is routine. These 3 are the ones most likely to cause trouble here. The rest are minor; they're under "Show everything".
If the event loop is destroyed while async Redis operations are pending, the adapter will attempt to use freed memory, causing crashes or memory corruption
Race condition where the main context is accessed after the source is destroyed, leading to use-after-free crashes in the GLib event loop
In multi-threaded environments, concurrent histogram updates could corrupt the normalization calculation, leading to incorrect bucket indexing and data corruption
Show everything (9 more)
Assumes the counts array length (counts_len) matches the allocated size of the counts pointer, but the struct provides no built-in bounds checking
If this fails: Buffer overflows when accessing counts[index] if the array was resized without updating counts_len, leading to memory corruption or crashes
deps/hdr_histogram/hdr_histogram.h:hdr_histogram
Assumes 64-bit integers are naturally aligned on the target platform, relying only on compiler barriers rather than hardware-specific atomic operations
If this fails: On platforms where 64-bit loads aren't atomic (like 32-bit x86), torn reads could return partially updated values, corrupting histogram statistics
deps/hdr_histogram/hdr_atomic.h:hdr_atomic_load_64
Assumes Redis's zmalloc/zfree functions are compatible with standard malloc/free semantics and handle NULL pointers correctly
If this fails: If zmalloc has different behavior than standard malloc (like returning different error codes or handling alignment differently), histogram allocation could fail silently or corrupt memory
deps/hdr_histogram/hdr_redis_malloc.h:zmalloc
Assumes the iv_fd structure remains valid between the time it's configured with iv_fd_set_handler_in and when the ivykis event loop processes the event
If this fails: If the redisIvykisEvents structure is freed before ivykis processes pending events, the event handler will be called with a dangling pointer, causing crashes
deps/hiredis/adapters/ivykis.h:redisIvykisAddRead
Assumes the libev event loop and the Redis async context have synchronized lifetimes, with no mechanism to handle cases where one is destroyed before the other
If this fails: Dangling pointers between the libev watchers and Redis context, potentially causing callbacks to be invoked on freed memory
deps/hiredis/adapters/libev.h:redisLibevEvents
Assumes significant_figures parameter is between 1 and 5, but the histogram constructor may not validate this range
If this fails: Values outside this range could cause integer overflow in bucket calculations or create histograms with unexpected memory usage patterns
deps/hdr_histogram/hdr_histogram.h:significant_figures
Assumes the platform's stdint.h provides exactly the same integer types as expected by the Grisu algorithm's bit manipulation
If this fails: On exotic platforms with different integer representations, the floating-point conversion could produce incorrect decimal strings
deps/fpconv/fpconv_powers.h:stdint.h
Assumes GLib's poll event constants (G_IO_IN, G_IO_OUT) map correctly to the underlying system's poll/epoll constants
If this fails: Incorrect event monitoring if GLib's constants don't match system expectations, leading to missed read/write readiness events
deps/hiredis/adapters/glib.h:G_IO_IN
Assumes compiler memory barriers (_ReadBarrier, _WriteBarrier) provide sufficient ordering guarantees for atomic operations without hardware memory barriers
If this fails: On weakly-ordered architectures, the CPU might reorder memory operations despite compiler barriers, leading to race conditions in histogram updates
deps/hdr_histogram/hdr_atomic.h:_ReadBarrier
See the full structural analysis of redis: the pipeline, data models, and system behavior that put these assumptions in context.
Full analysis of redis/redis →Frequently Asked Questions
What does redis assume that could break in production?
The one most likely to cause trouble: Assumes the Redis event loop (aeEventLoop) will remain valid for the entire lifetime of the redisAsyncContext, with no validation that the event loop hasn't been destroyed If this fails, If the event loop is destroyed while async Redis operations are pending, the adapter will attempt to use freed memory, causing crashes or memory corruption
How many hidden assumptions does redis have?
CodeSea found 12 assumptions redis relies on but never validates, 4 of them critical, spanning Resource, Temporal, Contract, Shape, Domain, Scale, Environment, Ordering. Most are routine — the analysis flags the two or three most likely to actually bite.
What is a hidden assumption?
Something the code depends on but never checks: a data shape, an ordering, an environment condition, a scale limit, or a contract with another service. It holds until the world it runs in changes, then fails silently.