612766 - Clone readonly database connections

Status: RESOLVED WORKSFORME

(Firefox :: Sync, defect)

Description

[Philipp von Weitershausen [:philikon]]

After bug 552023 lands in m-c we can clone read only database connections to avoid lock contentions.

Comment 1

[Mike Connor [:mconnor]]

Which connections would we want as readonly?

Comment 2

[Richard Newman [:rnewman]]

(In reply to Mike Connor [:mconnor] from comment #1)
> Which connections would we want as readonly?

E.g.,

http://hg.mozilla.org/mozilla-central/file/1c7e1db3645b/toolkit/components/places/History.cpp#l1391

If you mean "in Sync": consider that a huge amount of the work Sync does -- building metadata, uploading records, and reconciling incoming records -- can all be done read-only. A user's primary profile downloads and applies very few unreconciled records.

The theory is that doing these on a read-only DB connection will allow the rest of the system to avoid contention.

Comment 3

[Marco Bonardo [:mak]]

(In reply to Richard Newman [:rnewman] from comment #2)
> The theory is that doing these on a read-only DB connection will allow the
> rest of the system to avoid contention.

Right, a connection clone increases concurrency on databases using WAL, at expense of using more memory though, since each connection has its own page cache.

Comment 5

[Richard Newman [:rnewman]]

Bug 660044 has a WIP patch that might be interesting.

Comment 6

[Lina Butler [:lina]]

Sync now uses public Places APIs.