IEEE 47th - 香港大学 Detecting Hidden Failures of DBMS, A Comprehensive Metamorphic Relation Output Patterns Approach.pdf

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Detecting Hidden Failures of DBMS:

A Comprehensive

Metamorphic Relation Output Patterns Approach

Matthew Siu-Hin Tang

Department of Computer Science

The Univeristy of Hong Kong

Pokulam, Hong Kong

tshcat@connect.hku.hk

T. H. Tse*

Department of Computer Science

The University of Hong Kong

Pokulam, Hong Kong

thtse@cs.hku.hk

Zhi Quan Zhou

School of Computing and IT, University of Wollongong

Wollongong NSW 2522, Australia, and

Alibaba and Ant Group, Hangzhou, China

zhiquan@uow.edu.au

Abstract—The testing of large databases faces the test oracle

problem, namely, that it is difficult to verify execution results

against expected outcomes. Rigger and Su applied metamorphic

testing through query partitioning and ternary logic partitioning

techniques to alleviate the challenge. In Part (A) of our project, we

conduct an in-depth investigation and have identified a gap

between the two techniques. We propose a disjoint partitioning

approach to address it. In Part (B), we conduct a comprehensive

investigation into the metamorphic testing of DBMS by comparing

disjoint partitioning with metamorphic relation output patterns

(MROPs) by Segura et al. We propose an exhaustive collection of

MROPs for DBMS. To the best of our knowledge, this is the first

project to integrate in-depth and comprehensive approaches to

tackle the diverse challenges in DBMS testing. In Part (C), we

conduct an empirical case study of their applications to

OceanBase, the DBMS associated with the world’s fastest online

transaction processing system. Although OceanBase has been

extensively tested and widely used in the industry, we have

detected 12 hidden failures and 8 new crashes.

Index Terms—test oracle, metamorphic testing, metamorphic

relation output pattern, DBMS, SQL, OceanBase

I. INTRODUCTION

Because of the popularity of online transaction processing

(OLTP) systems [1] in the financial sector, the correctness of the

supporting database management system (DBMS) is crucial.

However, owing to the scale of large databases, the testing of

DBMS is challenging [2]. It faces the test oracle problem, which

refers to the difficulty in verifying system execution results [3]

[4]. The metamorphic testing (MT) methodology [5][6][7] was

invented in 1998 to alleviate the problem. In 2020, Rigger and

Su [8] applied MT to address the issue in DBMS testing through

the query partitioning (QP) and ternary logic partitioning (TLP)

techniques. Empirical studies showed that they revealed 175

failures in five DBMS.

Our current project is divided into three parts. In Part (A),

we conduct an in-depth investigation on [8]. We find a gap

between QP and TLP, and introduce the concept of disjoint par-

titioning (DP) to tackle the issue. In Part (B), we conduct a com-

prehensive investigation of the adequacy of the metamorphic

relations constructed via DP, comparing them with the metamor-

phic relation output patterns (MROPs) proposed by Segura et al.

[9]. We propose a more comprehensive approach for classifying

and constructing metamorphic relations in DBMS testing. In

Part (C) of the project, we perform an empirical case study on

OceanBase [10], which has been developed by the Alibaba and

Ant Group and associated with the world’s fastest OLTP [11].

We apply both the in-depth and comprehensive approaches to

test OceanBase, and have detected 12 hidden failures and 8 new

crashes.

II. PART (A): IN-DEPTH INVESTIGATION INTO

METAMORPHIC TESTING OF DBMS

A. Motivation Example

Consider the staff table on the right.

Let us write a SELECT statement in

SQL:

SELECT * FROM staff WHERE salary < 5000;

Suppose the DBMS returns the result

on the right. It reveals a failure because

Bob also has a salary lower than 5000

and is missing from the list.

Imagine that the staff table contains 10 000 records instead

of only three. We execute the same SQL SELECT statement

against the DBMS to list all the staff with a salary lower than

5000. Suppose the DBMS returns a list of 3000 staff. This time,

we cannot easily tell whether the result of 3000 staff misses any

legitimate record or contains any superfluous record. Owing to

the large volume of data, it is difficult to detect failures.

B. Metamorphic Testing

In software testing, a test oracle is the mechanism to verify

the execution result against the expected outcome [12]. The test

oracle problem refers to the situation where such a mechanism

is either missing or extremely difficult to apply [3][4]. As we

have observed in the motivating example, it would be challeng-

ing to verify the result of a given query in large databases.

In 1998, T. Y. Chen invented the metamorphic testing (MT)

methodology [5][6] [7] , which supports test case generation and

alleviates the test oracle problem. He defines metamorphic

* Corresponding author.

name

salary

Alice

5000

Charlie

2000

Bob

3000

name

salary

Charlie

2000

Postprint of paper in Proceedings of the IEEE 47th Annual International Computers, Software, and

Applications Conference Workshops (COMPSACW ’23), IEEE, Piscataway, NJ, USA (2023)

HKU CS Tech Report TR-2023-01

relations (MRs) as necessary properties of the target function or

program in relation to multiple inputs and their expected out-

puts. To conduct MT, some program inputs are first constructed

as original test cases (called source test cases). On the basis of a

target MR, new inputs are constructed as follow-up test cases.

Contrary to traditional testing, which verifies the correctness of

each individual test result, MT verifies the relation among the

source and follow-up inputs and outputs with respect to the MR.

About 500 papers on MT have been published. However,

research work on the application of MT to DBMS has been very

limited [8] [13][14].

When applying MT to DBMS testing, a source test case may

be an initial query whereas a follow-up test case may be a subse-

quent query constructed according to a target MR. Then, the

relationship between their outputs (resultant lists returned by the

DBMS) can be verified with reference to the MR. In the case of

the staff table example, we may specify an MR such that “if we

add one more condition to the query, the DBMS should return

fewer records.” For instance, we may refine our query to ask for

all the staff with salary < 5000 AND name = 'Alice'. On execu-

tion, if the DBMS returns 4000 staff, which is more than the

previous result, we say that there is a violation of the MR. It

indicates a failure of the DBMS. In this way, failures are

revealed using MT without the need for a test oracle.

C. Revisit of QP and TLP by Rigger and Su

Rigger and Su [8] proposed query partitioning (QP) and

ternary logic partitioning (TLP) for metamorphic testing of

DBMS. QP is a general strategic concept that describes an MR

among DBMS queries. Outputs of the follow-up queries are

non-overlapping sublists of the output of the source query. The

MR specifies that the concatenation of the outputs of the follow-

up queries must be the same as the output of the source query.

A violation of the MR indicates a failure.

TLP is a special case of QP. An original query is transformed

into three partitioning queries, which are three predicate variants

derived from a randomly generated predicate. Let us consider

the staff table again, with a source query to return all the staff.

We generate a random predicate name = 'Alice'. We derive three

partitioning queries with three predicate variants: name = 'Alice',

NOT (name = 'Alice'), and name = 'Alice' IS NULL. Since SQL is

based on ternary Boolean logic [14], we know that name = 'Alice'

can be TRUE, FALSE, or NULL, falling into the resultant lists of

the three partitioning queries. Hence, following the MR stated in

QP, by concatenating the three resultant lists, we should obtain

the result of the original query, namely, all the staff in the table.

TLP has revealed 175 failures in five DBMS, including SQLite,

MySQL, CockroachDB, TiDB, and DuckDB.

D. Extension of QP and TLP to Disjoint Partitioning

Our thorough investigation reveals that the high-level QP is

too general for practical MR construction, while the low-level

TLP is too specific. We propose an innovative technique called

disjoint partitioning (DP) to fill the gap. The core idea is that

resultant lists returned by the DBMS can be divided into

exhaustive and mutually exclusive partitions using, for

instance, the SQL keywords LIMIT and OFFSET. For example,

given a staff table with 100 rows, we can write two queries

(Q0.1) SELECT * FROM staff LIMIT 50 OFFSET 0;

(Q0.2) SELECT * FROM staff LIMIT 50 OFFSET 50;

to return two resultant sublists, each containing the first and last

50 staff in the table, respectively.

Consider the entry_exit table below, recording the id, name,

and entry_exit_count of 10 000 staff in a large corporation:

name

entry_exit_count

Alice

...

10000

Dave

By examining the entry_exit_count for each staff, we can

determine that those with odd values are inside the building,

whereas those with even values are outside.

We can use the SQL bitwise and (&) operator with a constant

operand 1 to determine whether an entry_exit_count is odd or

even. An odd number & 1 returns an integer 1, and an even

number & 1 returns an integer 0.

Hence, we can write the following statement in OceanBase

DBMS to find all the staff (whose entry_exit_count is an odd

number) inside the building:

(Q1.1) SELECT * FROM entry_exit

WHERE entry_exit_count & 1;

OceanBase returns a list with 3000 staff. However, we do not

know whether the list of 3000 records is correct, because we do

not have a test oracle.

In DP , we propose follow-up queries such that they partition

list of rows in the original table into disjoint portions and apply

the same WHERE condition. We write the two follow-up queries

as follows:

(Q1.2) SELECT * FROM (SELECT * FROM entry_exit

LIMIT 5000 OFFSET 0) AS offset1

WHERE entry_exit_count & 1;

(Q1.3) SELECT * FROM (SELECT * FROM entry_exit

LIMIT 5000 OFFSET 5000) AS offset2

WHERE entry_exit_count & 1;

Query (Q1.2) retrieves the staff with an odd entry_exit_count

in rows 1 to 5000, whereas query (Q1.3) retrieves those in rows

5001 to 10 000. OceanBase returns 1500 and 1501 staff, respec-

tively.

The MR states that simple concatenation of the outputs of

follow-up queries (Q1.2) and (Q1.3) should produce the same

result as the original query (Q1.1). The MR is therefore violated

because there are more rows in the concatenated output from

(Q1.2) and (Q1.3). Thus, we have revealed a hidden failure.

III. PART (B): COMPREHENSIVE INVESTIGATION INTO

METAMORPHIC TESTING OF DBMS

Although our previous extension [16] of Rigger and Su’s

work to DP reveals failures, it only tests for one kind of MR. In

order to identify more MRs in DBMS, we draw our inspiration

from existing MR frameworks from the literature.

This part of the project was published in [16].