Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/doc/dev/osd_internals/pg.rst b/doc/dev/osd_internals/pg.rst
new file mode 100644
index 000000000..397d4ab5d
--- /dev/null
+++ b/doc/dev/osd_internals/pg.rst
@@ -0,0 +1,31 @@
+====
+PG
+====
+
+Concepts
+--------
+
+*Peering Interval*
+  See PG::start_peering_interval.
+  See PG::acting_up_affected
+  See PG::PeeringState::Reset
+
+  A peering interval is a maximal set of contiguous map epochs in which the
+  up and acting sets did not change.  PG::PeeringMachine represents a
+  transition from one interval to another as passing through
+  PeeringState::Reset.  On PG::PeeringState::AdvMap PG::acting_up_affected can
+  cause the pg to transition to Reset.
+  
+
+Peering Details and Gotchas
+---------------------------
+For an overview of peering, see `Peering <../../peering>`_.
+
+  * PG::flushed defaults to false and is set to false in
+    PG::start_peering_interval.  Upon transitioning to PG::PeeringState::Started
+    we send a transaction through the pg op sequencer which, upon complete,
+    sends a FlushedEvt which sets flushed to true.  The primary cannot go
+    active until this happens (See PG::PeeringState::WaitFlushedPeering).
+    Replicas can go active but cannot serve ops (writes or reads).
+    This is necessary because we cannot read our ondisk state until unstable
+    transactions from the previous interval have cleared.