Message-ID: <gh-pgjdbc-pgjdbc-2918-c1632056820@github.com>
From: "zhurs (@zhurs)" <noreply+zhurs@github.com>
To: "pgjdbc/pgjdbc" <noreply+pgjdbc-pgjdbc@github.com>
Date: Wed, 12 Jul 2023 08:16:33 +0000
Subject: Re: [pgjdbc/pgjdbc] issue #2918: Set defaultRowFetchSize=10000 by default to improve app stability
In-Reply-To: <gh-pgjdbc-pgjdbc-2918@github.com>
References: <gh-pgjdbc-pgjdbc-2918@github.com>
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It seems that it is an incompatible change - for insert..returning statements, if the size of the result is more than fetchSize method executeUpdate returns -1, here is a small example:

```java
conn.prepareStatement("DROP TABLE IF EXISTS test_table").execute();
conn.prepareStatement("CREATE TABLE IF NOT EXISTS test_table (id SERIAL PRIMARY KEY, cnt INT NOT NULL)").execute();

for (var fetchSize : List.of(0, 1, 2, 3)) {
    System.out.println("FetchSize=" + fetchSize);

    try (var stmt = conn.prepareStatement("INSERT INTO test_table (cnt) VALUES (1), (2) RETURNING id", RETURN_GENERATED_KEYS)) {
        stmt.setFetchSize(fetchSize);

        var ret = stmt.executeUpdate();
        System.out.println("executeUpdate result: " + ret);

        var rs = stmt.getGeneratedKeys();
        System.out.print("ids: ");
        while (rs.next()) {
            System.out.print(rs.getInt(1) + " ");
        }
        System.out.print("\n\n");
    }
}
```

Output:
```
FetchSize=0
executeUpdate result: 2
ids: 1 2 

FetchSize=1
executeUpdate result: -1
ids: 3 4 

FetchSize=2
executeUpdate result: -1
ids: 5 6 

FetchSize=3
executeUpdate result: 2
ids: 7 8 
```

Also, -1 is not documented and contradicts with jdbc specification:

> executeUpdate Returns:
> either (1) the row count for SQL Data Manipulation Language (DML) statements or (2) 0 for SQL statements that return nothing