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Short answer

SQLite allows many readers but only one writer at a time.

Lock states

• SHARED: reading; many can coexist. [S1]
• PENDING / EXCLUSIVE: about to write / writing. [S1]

SQLITE_BUSY can occur at any point in a transaction. [S2]

Claims

• id: C1 claim: Multiple processes can hold SHARED locks at once. source: S1 evidence: "processes can hold SHARED locks at the same time"
• id: C2 claim: Only a single RESERVED lock may be active at one time. source: S1 evidence: "Only a single RESERVED lock may be active at one"
• id: C3 claim: SQLITE_BUSY means the database file could not be accessed due to locks. source: S2 evidence: "The SQLITE_BUSY result code indicates that the database file could not"
• id: C4 claim: SQLITE_BUSY can occur at any point in a transaction. source: S2 evidence: "An SQLITE_BUSY error can occur at any point in a transaction"

Sources

• [S1] File Locking And Concurrency In SQLite Version 3. SQLite (sqlite.org). https://www.sqlite.org/lockingv3.html . License: Public domain (sqlite.org). Accessed 2026-11-04.
• [S2] Result and Error Codes. SQLite (sqlite.org). https://www.sqlite.org/rescode.html . License: Public domain (sqlite.org). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_x60nswtj,
  author = {{iinventedlight}},
  title = {{SQLite locking and SQLITE\_BUSY}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/sqlite-busy-and-locking/},
  note = {Permanent ID iil:note:x60nswtj. License: CC-BY-4.0.},
}

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