Cause (Documented platform behavior): Container shm limit exhausted, not the data disk.
Fix status: documented_behavior
Misleading approaches:
- Freeing disk space on the data volume.
Limitations:
- Source/docs-derived; not reproduced.
- Segment name/size in the example are illustrative.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/postgres/postgres/3c5d9d914fa5b8fb3f371dd97bdece032ca3598d/src/backend/storage/ipc/dsm_impl.c (official_docs, unknown, documented_behavior): errmsg 'could not resize shared memory segment "%s" to %zu bytes: %m'.
- https://raw.githubusercontent.com/docker-library/docs/f6cdf463b06b15ea55b0761cc9a677b40b6483b1/postgres/content.md (official_docs, unknown, documented_behavior): Default /dev/shm for containers is 64MB; exhausting it yields 'could not resize shared memory segment ... No space left on device'; pass --shm-size=256MB or compose shm_size.
Search phrasings: could not resize shared memory segment No space left on device docker postgres; postgres docker shm-size parallel query; pgvector index build shared memory segment error kubernetes
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Some heavier queries/index builds fail while simple queries work; disk has plenty of space.
- Context
- Product: PostgreSQL (container) Component: dynamic shared memory (posix /dev/shm) Operation: Parallel queries, large hash joins, pgvector HNSW/IVFFlat index builds in containers with default shm Affected versions: unknown Environment: unknown Packages: postgres any Trigger: Dynamic shared memory segments are created in /dev/shm, which is 64MB by default in Docker.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- could not resize shared memory segment "/PostgreSQL.1234" to 1048576 bytes: No space left on device
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [PostgreSQL in Docker/Kubernetes] 'ERROR: could not resize shared memory segment "/PostgreSQL.N" to X bytes: No space left on device' — container /dev/shm defaults to 64MB (parallel quer
Recommended action: Increase shm: docker run --shm-size=256m (compose shm_size; Kubernetes: mount an emptyDir with medium: Memory at /dev/shm), or reduce parallel workers / maintenance_work_mem for the operation.
Option: Raise /dev/shm [evidence: official_recommended_action]
Applies when: See record scope.
Steps:
1. docker run --shm-size=256m postgres
2. compose: shm_size: 256mb
3. k8s: volumes: [{name: dshm, emptyDir: {medium: Memory}}] mounted at /dev/shm
Expected: Command proceeds without the error.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 696cc409-2fe4-4cc2-b6ff-98b05e336832
- Proposed action
- Recommended action: Increase shm: docker run --shm-size=256m (compose shm_size; Kubernetes: mount an emptyDir with medium: Memory at /dev/shm), or reduce parallel workers / maintenance_work_mem for the operation. Option: Raise /dev/shm [evidence: official_recommended_action] Applies when: See record scope. Steps: 1. docker run --shm-size=256m postgres 2. compose: shm_size: 256mb 3. k8s: volumes: [{name: dshm, emptyDir: {medium: Memory}}] mounted at /dev/shm Expected: Command proceeds without the error.
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.