feat(store): expose mmap_size via CBM_SQLITE_MMAP_SIZE env#315
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DeusData merged 1 commit intoDeusData:mainfrom May 10, 2026
Merged
feat(store): expose mmap_size via CBM_SQLITE_MMAP_SIZE env#315DeusData merged 1 commit intoDeusData:mainfrom
DeusData merged 1 commit intoDeusData:mainfrom
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Hard-coded `PRAGMA mmap_size = 67108864` in configure_pragmas() left no path for users running multiple cbm-mcp instances against the same cache to opt out of memory-mapped I/O. On macOS, when one instance's checkpoint or reindex truncates the DB file under another instance's live mmap, accessing the now-missing pages raises SIGBUS, taking the process down. Setting CBM_SQLITE_MMAP_SIZE=0 reverts to read()/pread() I/O, which returns recoverable SQLITE_IOERR instead of crashing the process. - Default unchanged (67108864 / 64 MB). No behavior change for single-instance users. - Malformed values (non-numeric, partial-numeric) fall back to the default rather than failing the store open. - Negative values clamp to 0. - New tests: tests/test_store_pragmas.c covers all five resolver paths plus an integration smoke that opens a file-backed store with mmap disabled. Empirical evidence: 9 SIGBUS crash reports collected on macOS arm64 v0.6.0 in a 14-hour window, all signature 'cluster_pagein past EOF' with stacks bottoming in SQLite btree code under the watcher thread's incremental-index pipeline.
DeusData
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enhancement
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Merged via rebase, thanks @edwardmhughes. Diagnosis is precise — the macOS SIGBUS-on-truncated-mmap interaction is exactly the kind of failure mode that needs a knob rather than a code fix, since the safe-by-default value ( The implementation is solid:
Test coverage is comprehensive — 7 cases covering default/zero/explicit/negative/garbage/partial-garbage/integration-smoke. The integration smoke test (opening a file-backed store with Issue #314 auto-closed with the merge. |
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Summary
Hard-coded
PRAGMA mmap_size = 67108864left no path for users running multiplecodebase-memory-mcpinstances against the same cache to opt out of memory-mapped I/O.On macOS, when one instance's checkpoint or reindex truncates the DB file under another instance's live mmap, accessing the now-missing pages raises
SIGBUS, which takes down the process. SettingCBM_SQLITE_MMAP_SIZE=0reverts toread()/pread()I/O, which returns recoverableSQLITE_IOERRinstead.Changes
src/store/store.c: Extractscbm_store_resolve_mmap_size()— readsCBM_SQLITE_MMAP_SIZE, validates withstrtoll, clamps negative to 0, falls back to default67108864on missing/malformed inputsrc/store/store.h: Declarescbm_store_resolve_mmap_size()for teststests/test_store_pragmas.c(new): 7 tests covering default, zero, explicit value, negative clamp, garbage input, partial garbage, and store-open smoke testMakefile.cbm+tests/test_main.c: Wire new test suiteBehavior
CBM_SQLITE_MMAP_SIZEunsetPRAGMA mmap_size = 67108864CBM_SQLITE_MMAP_SIZE=0PRAGMA mmap_size = 0(disables mmap)CBM_SQLITE_MMAP_SIZE=1048576PRAGMA mmap_size = 1048576Single-instance users: no behavior change.
Fixes #314