auto

notes/hat.md

@@ -81,7 +81,7 @@ guarantees. Assume invariant *x == y*:
 Both preserve consistency in isolation, but not w/ this schedule and dirty writes.	 
 
 
-## Isolation guarantee definitions:
+## Achievable isolation levels with partitions
 
 "**read uncommitted**" (PL-1)
 - writes to each obj totally ordered (prohibits dirty writes)
@@ -100,12 +100,12 @@ Both preserve consistency in isolation, but not w/ this schedule and dirty write
 - **item cut isolation** 
   - multiple different values
   - implement by buffering reads
-- **predicate cut isolation*
+- **predicate cut isolation**
   - cut over "SELECT ..WHERE....")  (phantom anomalies)
   - implement by caching entire logical ranges
 
 ----
-### Unachievable isolation levels with partitions:
+## Unachievable isolation levels with partitions
 - snapshot isolation,
   - read from consistent cut
   - commit only if items from writeset not committed by another T since snapshot
@@ -116,6 +116,10 @@ Both preserve consistency in isolation, but not w/ this schedule and dirty write
     on entire set of results
   - violated if lost writes because of locks not reaching across partition.
   - therefore not HAT (because can't prevent lost updates)
+- Serializability:
+  - optimistic requires global validation
+  - pessimistic requires global coord/locking
+
 ----
 ### Unachievable properties
 - preventing lost updates
@@ -129,27 +133,17 @@ Both preserve consistency in isolation, but not w/ this schedule and dirty write
 
   *Clearly impossible to prevent in dist environment.*
   
-- preventing write skew.  Write Skew generalizes LU to multiple keys. Possible problem is
-violation of consistency, such as "x == y""
+- preventing write skew.
+  - generalizes *lost updates* to multiple keys
+  - problem is possible violation of *consistency* (different Tx effective
+    access distinct replicas)
+  - initially X = 1, Y = 2, each transaction trying to make them identical.
 ```
      T1: t = x;  y = t
      T2: t = y;  x = t
 ```
 Can happen w/ snapshot isolation even w/o partitions.
 
-- Serializability:
-  - optimistic requires global validation
-  - pessimistic requires global coord/locking
-
-
-
-- Katura not buying sticky avail (definitional)
-- Nao -  "really confusing"  (yes)
-- Patrick/Andrew - causal only w/ sticky (client caching breaks lots of guarantees)
-
-
-
-----
 
 ### HAT-compliant: