src: add a checker for comments test

Closes #32

CHANGELOG.md

@@ -10,6 +10,8 @@ change log follows the conventions of
 
 ### Added
 
+- Add a checker for comments test (#32).
+
 ### Fixed
 
 - Fixed defaults for anomalies in a README.

README.md

@@ -271,6 +271,34 @@ Example of history:
 {:type :invoke, :f :release, :process 0, :time 679093895, :index 10}
 ```
 
+### custom-comments
+
+A custom checker for a comments histories.
+
+Imagine an application which has a sequential stream of comments. Users make
+comments by inserting new rows into a table. Because each request is
+load-balanced to a different server, two transactions from the same user may
+execute on different nodes. Now imagine that a user makes a comment `C1` in
+transaction `T1`. `T1` completes successfully. The user then realizes they made
+a mistake, and posts a correction comment `C2`, in transaction `T2`. Meanwhile,
+someone attempts to read all comments in a third transaction `T3`, concurrent
+with both `T1` and `T2`.
+
+Example of history:
+
+```clojure
+{:index 1, :type :invoke :f :read   :value nil}
+{:index 2, :type :invoke :f :write  :value 425}
+{:index 3, :type :ok     :f :write  :value 425}
+{:index 4, :type :invoke :f :write  :value 430}
+{:index 5, :type :ok     :f :write  :value 430}
+{:index 6, :type :ok     :f :read   :value #{2 10 15 20 34 35 38 42 43 47 51 53 59 61 71 72 82 88 89
+                                           113 119 123 129 132 145 146 163 167 176 206 216 224 230
+                                           238 243 244 255 260 292 294 299 312 316 324 325 327 330
+                                           350 356 359 360 361 363 366 367 371 376 403 410 419 422
+                                           430}}
+```
+
 ## License
 
 Copyright © 2021-2022 Sergey Bronnikov

histories/custom/comments.edn

@@ -0,0 +1,10 @@
+{:index 1, :type :invoke :f :read   :value nil}
+{:index 2, :type :invoke :f :write  :value 425}
+{:index 3, :type :ok     :f :write  :value 425}
+{:index 4, :type :invoke :f :write  :value 430}
+{:index 5, :type :ok     :f :write  :value 430}
+{:index 6, :type :ok     :f :read   :value #{2 10 15 20 34 35 38 42 43 47 51 53 59 61 71 72 82 88 89
+                                           113 119 123 129 132 145 146 163 167 176 206 216 224 230
+                                           238 243 244 255 260 292 294 299 312 316 324 325 327 330
+                                           350 356 359 360 361 363 366 367 371 376 403 410 419 422
+                                           430}}

src/elle_cli/cli.clj

@@ -10,6 +10,7 @@
             [jepsen [checker :as jepsen-model]]
             [jepsen.tests.bank :as jepsen-bank]
             [jepsen.tests.long-fork :as jepsen-long-fork]
+            [elle-cli.comments :as comments-model]
             [elle.list-append :as elle-list-append]
             [elle.rw-register :as elle-rw-register]
             [elle.consistency-model :as elle-consistency-model]
@@ -80,6 +81,7 @@
    "jepsen-counter"          jepsen-model/counter
    "jepsen-set"              jepsen-model/set
    "jepsen-set-full"         jepsen-model/set-full
+   "custom-comments"         comments-model/checker
    "elle-rw-register"        elle-rw-register/check
    "elle-list-append"        elle-list-append/check})
 
@@ -157,6 +159,7 @@
         "  knossos-register - a Knossos checker for write-read registers."
         "  knossos-cas-register - a Knossos checker for CAS (Compare-And-Set) registers."
         "  knossos-mutex - a Knossos checker for a mutex histories."
+        "  custom-comments - a custom checker for a comments histories."
         ""
         "Options:"
         options-summary
@@ -171,6 +174,9 @@
     (case checker-group
        "knossos" (competition/analysis (checker-fn) history)
        "elle" (checker-fn options history)
+       "custom" (case model-name
+                  "custom-comments" (checker-fn)
+                 )
        "jepsen" (case model-name
                   "jepsen-bank" (jepsen-model/check-safe (checker-fn {:negative-balances? true}) nil history)
                   "jepsen-set-full" (jepsen-model/check-safe (checker-fn) nil history)

src/elle_cli/comments.clj

@@ -0,0 +1,88 @@
+(ns elle-cli.comments
+  "Checks for a strict serializability anomaly in which T1 < T2, but T2 is
+  visible without T1.
+  We perform concurrent blind inserts across n tables, and meanwhile, perform
+  reads of both tables in a transaction. To verify, we replay the history,
+  tracking the writes which were known to have completed before the invocation
+  of any write w_i. If w_i is visible, and some w_j < w_i is *not* visible,
+  we've found a violation of strict serializability.
+  Splits keys up onto different tables to make sure they fall in different
+  shard ranges"
+  (:require [jepsen.checker :as checker]
+            [knossos.model :as model]
+            [knossos.op :as op]))
+
+(defprotocol Checker
+  (check [checker test history opts]
+         "Verify the history is correct. Returns a map like
+         {:valid? true}
+         or
+         {:valid?       false
+          :some-details ...
+          :failed-at    [details of specific operations]}
+         Opts is a map of options controlling checker execution. Keys include:
+         :subdirectory - A directory within this test's store directory where
+                         output files should be written. Defaults to nil."))
+
+(defn checker
+  "An empty checker that only returns nil."
+  []
+  (reify Checker
+    (check [_ _ _ _])))
+
+(comment
+; Source: https://github.com/jepsen-io/jepsen/blob/main/cockroachdb/src/jepsen/cockroach/comments.clj
+(defn checker
+  []
+  (reify Checker
+    (check [this test model history opts]
+      ; Determine first-order write precedence graph
+      (let [expected (loop [completed  (sorted-set)
+                            expected   {}
+                            [op & more :as history] history]
+                       (cond
+                         ; Done
+                         (not (seq history))
+                         expected
+
+                         ; We know this value is definitely written
+                         (= :write (:f op))
+                         (cond ; Write is beginning; record precedence
+                               (op/invoke? op)
+                               (recur completed
+                                      (assoc expected (:value op) completed)
+                                      more)
+
+                               ; Write is completing; we can now expect to see
+                               ; it
+                               (op/ok? op)
+                               (recur (conj completed (:value op))
+                                      expected more)
+
+                               true
+                               (recur completed expected more))
+
+                         true
+                         (recur completed expected more)))
+            errors (->> history
+                        (r/filter op/ok?)
+                        (r/filter #(= :read (:f %)))
+                        (reduce (fn [errors op]
+                                  (let [seen         (:value op)
+                                        our-expected (->> seen
+                                                          (map expected)
+                                                          (reduce set/union))
+                                        missing (set/difference our-expected
+                                                                seen)]
+                                    (if (empty? missing)
+                                      errors
+                                      (conj errors
+                                            (-> op
+                                                (dissoc :value)
+                                                (assoc :missing missing)
+                                                (assoc :expected-count
+                                                       (count our-expected)))))))
+                                []))]
+        {:valid? (empty? errors)
+         :errors errors}))))
+)

test.sh

@@ -38,3 +38,5 @@ $ELLE_CLI_BIN $ELLE_CLI_OPT jepsen-set-full histories/jepsen/set_full.json
 
 $ELLE_CLI_BIN $ELLE_CLI_OPT jepsen-bank histories/jepsen/bank.edn
 $ELLE_CLI_BIN $ELLE_CLI_OPT jepsen-bank histories/jepsen/bank.json
+
+$ELLE_CLI_BIN $ELLE_CLI_OPT custom-comments histories/custom/comments.edn