[YSQL] DELETE doesn't work when specifying a float key via JDBC

[komamitsu]

Jira Link: DB-7435

Description

I noticed DELETE statement in YugabyteDB can't delete records when specifying a float key via JDBC.

I think you can reproduce this issue using the following code.

package org.example;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.function.Supplier;

public class Main {

  public static void main(String[] args) throws SQLException {
//    Supplier<Connection> connFactory = ConnectionUtils.forPg();
    Supplier<Connection> connFactory = ConnectionUtils.forYugabyte();

    float key = 3.141592f;
    try (Connection conn = connFactory.get();
        Statement stmt = conn.createStatement()) {
      stmt.execute("CREATE TABLE IF NOT EXISTS float_tbl (pk double precision PRIMARY KEY)");
    }

    try (Connection conn = connFactory.get();
        PreparedStatement ps = conn.prepareStatement("INSERT INTO float_tbl (pk) VALUES (?)")) {
      ps.setFloat(1, key);
      System.out.println("inserted: " + ps.executeUpdate());
    }

    try (Connection conn = connFactory.get();
        PreparedStatement ps = conn.prepareStatement("DELETE FROM float_tbl WHERE pk = ?")) {
      ps.setFloat(1, key);
      System.out.println("deleted: " + ps.executeUpdate());
    }

    try (Connection conn = connFactory.get();
        PreparedStatement ps = conn.prepareStatement("SELECT pk FROM float_tbl WHERE pk = ?")) {
      ps.setFloat(1, key);
      ResultSet resultSet = ps.executeQuery();
      if (resultSet.next()) {
        System.out.println("selected value: " + resultSet.getFloat(1));
      }
      else {
        System.out.println("no selected value");
      }
    }
  }
}

This code creates a table that has a float primary key column, inserts a record and tries to delete the record. But the DELETE statement doesn't delete the record, while it works with PostgreSQL.

• With YugabyteDB

> Task :Main.main()
inserted: 1
deleted: 0
selected value: 3.141592

• With PostgreSQL

> Task :Main.main()
inserted: 1
deleted: 1
no selected value

I'm using YugabyteDB v2.19.0.0-b190.

Warning: Please confirm that this issue does not contain any sensitive information

• I confirm this issue does not contain any sensitive information.

[ddorian]

@komamitsu what version of postgresql did you use to test? Did you try with 11.x ?

[komamitsu]

@ddorian I used PostgreSQL 15.1.

[komamitsu]

I don't have a permission to the JIRA ticket, so could you tell me if there is any updates? Thanks.

[ddorian]

@komamitsu

The JIRA ticket is created automatically.

I've asked a developer to take a look at this.

I couldn't reproduce on python though.
yuga_float_check.py.zip

[komamitsu]

@ddorian Thanks for taking care of this issue.

BTW, I used Java 11 (Temurin) and PostgreSQL JDBC org.postgresql:postgresql:42.6.0 when I executed the above code.

[andrei-mart]

Due to internal precision errors in rounding up floating-point numbers it is always incorrect to test floats for exact equality.
It may fail quite randomly.
Use fixed point data type like numeric, or "almost equal" comparison.
Not an issue.

[komamitsu]

@andrei-mart Thanks for replying on this issue.

What I'm wondering is as follow

• This issue doesn't occur in PostgreSQL and even in MySQL
• The SELECT clause sees the key. But the DELETE clause can't find it. This is an inconsistent behavior
• The above code reproduces this issue 100%

And I didn't get what you mean by "randomly" while this issue doesn't happen at all in PostgreSQL.

I'm evaluating YugabyteDB for some reasons as a scalable PostgreSQL compatible database. But are you saying it's not compatible...?

[ddorian]

@komamitsu

This is a typical computer science problem.

And I didn't get what you mean by "randomly" while this issue doesn't happen at all in PostgreSQL.

Read https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-FLOAT , specifically this section:::

Comparing two floating-point values for equality might not always work as expected.

I can find the same thing in MYSQL docs https://dev.mysql.com/doc/refman/8.0/en/floating-point-types.html

Because floating-point values are approximate and not stored as exact values, attempts to treat them as exact in comparisons may lead to problems. They are also subject to platform or implementation dependencies.

---

So this is compatible with PostgreSQL. You just didn't hit it yet in PostgreSQL with your exact float-number above, but you will hit it, guaranteed, randomly.

[komamitsu]

@ddorian Thanks for pointing the documents. I agree with the difficulty in handling floating point types.

The SELECT clause sees the key. But the DELETE clause can't find it. This is an inconsistent behavior

So I guess YugabyteDB uses different ways to look up with float type key in SELECT and DELETE. But I think we don't need to discuss on this issue anymore.

[ddorian]

So I guess YugabyteDB uses different ways to look up with float type key in SELECT and DELETE

Are you guaranteed this won't happen in postgresql/mysql?