[
https://issues.apache.org/jira/browse/CASSANDRA-21505?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Minal Kyada reassigned CASSANDRA-21505:
---------------------------------------
Assignee: Minal Kyada
> PaxosV1MultiNodeTableWalkTest Failure - CAS on static column w/empty bytes
> --------------------------------------------------------------------------
>
> Key: CASSANDRA-21505
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21505
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Feature/Lightweight Transactions
> Reporter: C. Scott Andreas
> Assignee: Minal Kyada
> Priority: Normal
>
> {{PaxosV1MultiNodeTableWalkTest}} fails deterministically at a {{UPDATE ...
> IF <double static column> = <empty bytes>}} CAS. The Harry model predicts the
> CAS does not apply (expecting a failed-CAS result of {{{}[applied], s0,
> s1{}}}), while Paxos v1 applies it (returning {{[applied]}} only). The
> mismatch surfaces as an assertion in the model when it validates the returned
> rows against the expected columns.
> The disagreement is in how {{s1 = <empty bytes>}} is evaluated when {{s1}} is
> a {{double}} static column whose current value is empty bytes. This bug
> covers determining whether Paxos v1's evaluation or the Harry model's
> expectation is correct; and updating either the implementation or test.
>
> *Environment*
> * Apache Cassandra trunk at {{1332e21}}
> * {{CasMultiNodeTableWalkBase}} uses {{ReadRepairStrategy.NONE}} and
> {{paxos_variant = v1}} (this is a pure Paxos v1 path; no read repair).
> * Reproduced locally with JDK 11 (in-JVM dtest). Observed in CI on
> {{{}jvm21-dtests{}}}.
>
> *Reproducing*
> {{org.apache.cassandra.distributed.test.cql3.PaxosV1MultiNodeTableWalkTest}}
> (3-node cluster), pinned to the failing seed via the harness hook:
> // in
> PaxosV1MultiNodeTableWalkTest.preCheck(...):builder.withSeed(-570398361159823834L);
>
> then:
> {{ant test-jvm-dtest-some
> -Dtest.name=org.apache.cassandra.distributed.test.cql3.PaxosV1MultiNodeTableWalkTest
> -Dtest.methods=test}}
> It fails at step 387 (of 400) deterministically ({{{}Seed =
> -570398361159823834, Examples = 10{}}}).
>
> *Failure Observed*
> Schema:
> {{CREATE TABLE ks1.tbl (
> pk0 timeuuid, ck0 inet,
> s0 boolean static, s1 double static,
> v0 uuid, v1 frozen<set<frozen<tuple<float>>>>,
> PRIMARY KEY (pk0, ck0)
> )}}
> Shrunk operation history:
> {{INSERT INTO ks1.tbl (pk0, ck0, s0, s1, v0, v1)
> VALUES (00000000-0000-1200-b500-000000000000, '3484:...:762b', false,
> <empty bytes>, ...); -- s1 set to empty bytes
> ...}}
> {{UPDATE ks1.tbl SET s1 = <double> WHERE pk0 =
> 00000000-0000-1200-b500-000000000000
> IF s0 = false AND s1 = <empty bytes>;}}
>
> Model annotation for the CAS: "would apply false" (the model expects the
> condition to be false, so the CAS should not apply).
> Assertion (Harry model validating the returned rows):
> {{java.lang.AssertionError: actual rows do not match the schema [[applied],
> s0, s1];
> found [java.nio.HeapByteBuffer[pos=0 lim=1 cap=1]]
> at org.apache.cassandra.harry.model.ASTSingleTableModel
> (ASTSingleTableModel.java:1474)}}
>
> The model expected a failed-CAS result with three columns
> ({{{}[applied]=false{}}}, plus the current {{s0}} and {{{}s1{}}}), but the
> actual result had a single 1-byte value — the shape of a CAS that applied
> ({{{}[applied]=true{}}}).
>
> *Analysis*
> * The row's {{s1}} (a {{double}} static column) was written as empty bytes.
> The CAS condition compares {{{}s1 = <empty bytes>{}}}. Since the stored value
> equals the compared value, Paxos v1 evaluates the condition as true and
> applies the update (result {{{}[applied]{}}}, one column).
> * The Harry model evaluated the same condition as false (annotating "would
> apply false") and therefore expected the failed-CAS result shape
> {{{}[applied], s0, s1{}}}.
> * So the two disagree on the outcome of comparing a fixed-length numeric
> column to an empty-bytes value. Empty bytes for a fixed-length type
> ({{{}double{}}} is 8 bytes) is a degenerate value; the disagreement is in
> empty-value comparison semantics.
> Two possibilities:
> # Paxos v1 is correct (empty == empty, CAS applies) and the Harry model's
> condition evaluation for empty bytes on a fixed-length column is wrong (model
> bug in {{{}test/harry{}}}).
> # The Harry model is correct and Paxos v1 mis-evaluates the condition for an
> empty-bytes fixed-length column (product bug in the CAS condition path).
> Determining which requires comparing Cassandra's CQL semantics for {{= <empty
> bytes>}} on a {{{}double{}}}column against the model's evaluation, and
> checking whether the row's {{s1}} is treated as empty vs null.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
