Datastax cassandra 似乎缓存了 preparestatent

Question

当我的应用程序运行很长时间时，一切正常。但是当我将一列的类型从 int 更改为 text（删除 table 并重新创建）时，我发现了一个异常：

com.datastax.oss.driver.api.core.type.codec.CodecNotFoundException: Codec not found for requested operation: [INT <-> java.lang.String]
    at com.datastax.oss.driver.internal.core.type.codec.registry.CachingCodecRegistry.createCodec(CachingCodecRegistry.java:609)
    at com.datastax.oss.driver.internal.core.type.codec.registry.DefaultCodecRegistry.load(DefaultCodecRegistry.java:95)
    at com.datastax.oss.driver.internal.core.type.codec.registry.DefaultCodecRegistry.load(DefaultCodecRegistry.java:92)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3527)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2276)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2154)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$Segment.get(LocalCache.java:2044)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache.get(LocalCache.java:3951)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache.getOrLoad(LocalCache.java:3973)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4957)
    at com.datastax.oss.driver.shaded.guava.common.cache.LocalCache$LocalLoadingCache.getUnchecked(LocalCache.java:4963)
    at com.datastax.oss.driver.internal.core.type.codec.registry.DefaultCodecRegistry.getCachedCodec(DefaultCodecRegistry.java:117)
    at com.datastax.oss.driver.internal.core.type.codec.registry.CachingCodecRegistry.codecFor(CachingCodecRegistry.java:215)
    at com.datastax.oss.driver.api.core.data.SettableByIndex.set(SettableByIndex.java:132)
    at com.datastax.oss.driver.api.core.data.SettableByIndex.setString(SettableByIndex.java:338)

这个异常偶尔会出现。我正在使用 PreparedStatement 来执行查询，我认为它是从 DataStax 的驱动程序中缓存的。

我正在使用 AWS Keyspaces（Cassandra 版本 3.11.2）、DataStax 驱动程序 4.6。这是我的 application.conf:

  basic.request {
    timeout = 5 seconds
    consistency = LOCAL_ONE
  }
  advanced.connection {
    max-requests-per-connection = 1024
    pool {
      local.size = 1
      remote.size = 1
    }
  }
  advanced.reconnect-on-init = true
  advanced.reconnection-policy {
    class = ExponentialReconnectionPolicy
    base-delay = 1 second
    max-delay = 60 seconds
  }
  advanced.retry-policy {
    class = DefaultRetryPolicy
  }
  advanced.protocol {
    version = V4
  }
  advanced.heartbeat {
   interval = 30 seconds
   timeout = 1 second
  }
  advanced.session-leak.threshold = 8
  advanced.metadata.token-map.enabled = false
}

Answer 1

是的，Java 驱动程序 4.x 缓存准备好的语句 - 这与驱动程序 3.x 不同。来自 documentation:

the session has a built-in cache, it’s OK to prepare the same string twice.

...

Note that caching is based on: the query string exactly as you provided it: the driver does not perform any kind of trimming or sanitizing.

我不能 100% 确定源代码，但缓存中的相关条目可能不会在 table 删除时被清除。我建议打开 JIRA against Java driver，虽然这样的类型更改通常不被真正推荐 - 最好引入新类型的新字段，即使可以 re-create table.

Answer 2

没错。准备好的语句被缓存——这是使准备好的语句在被重用时更高效的优化，因为它们只需要准备一次（查询不需要再次解析）。

但我怀疑您案例中的潜在问题是您的查询涉及 SELECT *。最佳实践建议（无论您使用的是什么数据库）是显式枚举您从 table.

检索的列

在准备好的语句中，每个列都绑定到一个数据类型。当您通过 adding/dropping 列更改架构时，列的顺序（及其数据类型）不再与结果集的数据类型匹配，因此您最终会遇到驱动程序获得 int当它期待 text 或 vice-versa 时。干杯！

Datastax cassandra 似乎缓存了 preparestatent

Datastax cassandra seem to cache preparestatent

cassandra

datastax-java-driver