Use IN List Population in Your JDBC Application to Avoid Cursor Cache Contention Issues

Few developers are aware of a problem,那就是在SQL中使用INmay be encountered when listing "cursor cache contention "或 "Execution plan cache contention "的问题.This problem is described in detail in a previous article,It can be summed up like this.

All of these are differentSQL查询,Need to have a strong plan cacheRDBMS（例如Db2、Oracle、SQL Server）中被解析/计划/Cached execution plans that may differ：

SELECT * FROM t WHERE id IN (?);
SELECT * FROM t WHERE id IN (?, ?);
SELECT * FROM t WHERE id IN (?, ?, ?);
SELECT * FROM t WHERE id IN (?, ?, ?, ?);
SELECT * FROM t WHERE id IN (?, ?, ?, ?, ?);
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Although this is on the developer machine不是 问题,But it will be generated in production重大 问题.我见过这种情况,during peak loads,整个OracleInstances are paralyzed.虽然RDBMSSuppliers should strive to avoid serious problems that could result from this,But you can use us injOOQInvented a trick to fix it（Hibernate现在也有）.

IN 列表填充

这个技巧非常简单.只要将你的IN 列表 "填充 "到最接近的2 的幂数,Then repeat the last value,直到结束：

SELECT * FROM t WHERE id IN (?);                      -- Left as it is
SELECT * FROM t WHERE id IN (?, ?);                   -- Left as it is
SELECT * FROM t WHERE id IN (?, ?, ?, ?);             -- Padded 3 to 4
SELECT * FROM t WHERE id IN (?, ?, ?, ?);             -- Left as it is
SELECT * FROM t WHERE id IN (?, ?, ?, ?, ?, ?, ?, ?); -- Padded 5 to 8
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This is really a hack,There are better solutions to avoid this problem,包括使用数组或临时表,But your production system may be down,You need a quick fix.

从jOOQ 3.9（2016年底）开始,jOOQ已经支持IN The list fills for years,But with relatively new parsers and ParsingConnection ,You can now also in your nonjOOQsystem to any arbitrarySQLQueries apply this technique.这里有一个简单的例子：

// Any arbitrary JDBC Connection is wrapped by jOOQ here and replaced
// by a "ParsingConnection", which is also a JDBC Connection
DSLContext ctx = DSL.using(connection);
ctx.settings().setInListPadding(true);
Connection c = ctx.parsingConnection();

// Your remaining code is left untouched. It is unaware of jOOQ
for (int i = 0; i < 10; i++) {
    try (PreparedStatement s = c.prepareStatement(

        // This alone is reason enough to use jOOQ instead, 
        // but one step at a time :)
        "select 1 from dual where 1 in (" +
            IntStream.rangeClosed(0, i)
                     .mapToObj(x -> "?")
                     .collect(Collectors.joining(", ")) +
        ")")
    ) {
        for (int j = 0; j <= i; j++)
            s.setInt(j + 1, j + 1);

        try (ResultSet rs = s.executeQuery()) {
            while (rs.next())
                System.out.println(rs.getInt(1));
        }
    }
}
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The above example just builds and runs10a query of this form：

select 1 from dual where 1 in (?)
select 1 from dual where 1 in (?, ?)
select 1 from dual where 1 in (?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?)
select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
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But that's not what is being executed.在DEBUG日志中,我们可以看到以下内容：

Translating from         : select 1 from dual where 1 in (?)
Translating to           : select 1 from dual where 1 in (?)
Translating from         : select 1 from dual where 1 in (?, ?)
Translating to           : select 1 from dual where 1 in (?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
Translating from         : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
Translating to           : select 1 from dual where 1 in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
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就这样,Our legacy application is ready to run in production again,You will have time to address this more thoroughly.

结论

虽然jOOQMainly an interiorDSL,用于在JavaWrite type-safe embedded in SQL,But you can also base on anyJDBCuse it in many other applications.上面的例子是使用ParsingConnection ,It can parse all yoursSQL语句,and translate them/Convert to anything else,Including other dialects.