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penberg / limbo

Limbo is a work-in-progress, in-process OLTP database management system, compatible with SQLite.
MIT License
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Limbo acquires database file lock by default #302

Closed seonWKim closed 2 months ago

seonWKim commented 2 months ago

Question

Should we change current implementation of acquiring of lock when opening the database file?

Limbo implementation vs SQLite implementation

The impelmentations of IO's open_file acquires the database file lock by default. As a result, we are not able to open multiple connections like below

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The current implementation of SQLite seems to not acquire lock while opening the DB(It seems to acquire the database lock on non-SELECT transactions etc)

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Reference (SQLite Database System Design and Implementation (2nd Edition))

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penberg commented 2 months ago

@seonWKim We picked PRAGMA locking_mode = EXCLUSIVE as the default because it's the fastest one. With NORMAL (i guess same as NOLOCK there), the problem is that every transaction has to do a fcntl(), which is a round-trip to the kernel...

seonWKim commented 2 months ago

Oh I see. Will future implementation of transactions in limbo would not use fcntl() then?

penberg commented 2 months ago

Yes, exactly. Limbo would not need fcntl() in the transaction hot-path.