https://bugs.openldap.org/show_bug.cgi?id=10127

Issue ID: 10127 Summary: Thread Safety in LMDB with MDB_NOTLS and Readonly Cursors Product: LMDB Version: unspecified Hardware: All OS: All Status: UNCONFIRMED Keywords: needs_review Severity: normal Priority: --- Component: liblmdb Assignee: bugs@openldap.org Reporter: xiaoya2wei@gmail.com Target Milestone: ---

Greetings LMDB Community,

I am delving into the thread-safety aspects of LMDB, specifically regarding the use of readonly cursors across multiple threads. With the MDB_NOTLS flag enabled, which disables thread-local storage, my understanding is that readonly transactions may be shared between threads, provided there is proper synchronization to prevent concurrent access.

Building upon this, I seek clarity on the following: Can multiple threads safely access a single readonly cursor derived from such a synchronized readonly transaction when MDB_NOTLS is enabled?

Upon reviewing the LMDB source code, I noticed that cursors are tied to transactions (see mdb.c#L1335). This suggests that if threads can synchronously share a transaction, they might also share a cursor associated with it for data retrieval.

I recognize my analysis might be superficial, and I'm open to corrections. Your insights on this matter would be greatly appreciated to enhance my understanding of LMDB's concurrency mechanisms.

Thank you in advance for your assistance!