c# - Cassandra C# insert 似乎正在删除先前的数据？

Question

我创建了一个像这样的 cassandra 数据库:

cqlsh:timeseries> describe keyspace timeseries;

CREATE KEYSPACE timeseries WITH replication = {
  'class': 'SimpleStrategy',
  'replication_factor': '1'
};

USE timeseries;

CREATE TABLE option_data (
  ts timestamp,
  ask decimal,
  bid decimal,
  expiry timestamp,
  id text,
  strike decimal,
  symbol text,
  PRIMARY KEY ((ts))
) WITH
  bloom_filter_fp_chance=0.010000 AND
  caching='KEYS_ONLY' AND
  comment='' AND
  dclocal_read_repair_chance=0.100000 AND
  gc_grace_seconds=864000 AND
  index_interval=128 AND
  read_repair_chance=0.000000 AND
  replicate_on_write='true' AND
  populate_io_cache_on_flush='false' AND
  default_time_to_live=0 AND
  speculative_retry='99.0PERCENTILE' AND
  memtable_flush_period_in_ms=0 AND
  compaction={'class': 'SizeTieredCompactionStrategy'} AND
  compression={'sstable_compression': 'LZ4Compressor'};

CREATE TABLE underlying_data (
  symbol text,
  ask decimal,
  bid decimal,
  ts bigint,
  PRIMARY KEY ((symbol))
) WITH
  bloom_filter_fp_chance=0.010000 AND
  caching='KEYS_ONLY' AND
  comment='' AND
  dclocal_read_repair_chance=0.100000 AND
  gc_grace_seconds=864000 AND
  index_interval=128 AND
  read_repair_chance=0.000000 AND
  replicate_on_write='true' AND
  populate_io_cache_on_flush='false' AND
  default_time_to_live=0 AND
  speculative_retry='99.0PERCENTILE' AND
  memtable_flush_period_in_ms=0 AND
  compaction={'class': 'SizeTieredCompactionStrategy'} AND
  compression={'sstable_compression': 'LZ4Compressor'};

CREATE INDEX underlying_data_ts_idx ON underlying_data (ts);

cqlsh:timeseries>

我有一个 C# 函数:

public void InsertUnderlying(long timestamp, string symbol, decimal bid, decimal ask)
        {
            var batchStmt = new BatchStatement();
            var v2Insert = new SimpleStatement("insert into underlying_data " +
                "(ts, symbol, bid, ask) values(?, ?, ?, ?);");
            batchStmt.Add(v2Insert.Bind(timestamp, symbol, bid, ask));

            session.Execute(batchStmt);
        }

我实时调用这个函数来添加数据。但是，当我从 CQL 执行查询时，

cqlsh:timeseries> select * from underlying_data;

尽管我多次调用此函数，但我只看到一行。不确定如何附加数据而不是覆盖它？

Answer 1

在 Cassandra 中，主键是唯一的。您的表 underlying_data 仅在 symbol 列上键入:

PRIMARY KEY ((symbol))

这意味着特定符号的所有插入都将相互覆盖:

INSERT INTO underlying_data (symbol, ts, ask, bid) VALUES ('SPX',1412102636,3.1,4.0);
INSERT INTO underlying_data (symbol, ts, ask, bid) VALUES ('SPX',1412102708,3.0,4.4);
INSERT INTO underlying_data (symbol, ts, ask, bid) VALUES ('SPX',1412102731,2.1,5.0);

SELECT * FROM underlying_data;

 symbol | ts         | ask | bid
--------+------------+-----+-----
    SPX | 1412102731 | 2.1 | 5.0

要存储每个 INSERT，请将 ts 添加到主键定义中:

PRIMARY KEY (symbol, ts)

此外，Cassandra 不区分 INSERT 和 UPDATE(本质上是“UPSERT”)。虽然语法不同，但它们都完成相同的任务:存储特定键的列值。这意味着您可以使用 UPDATE 插入新记录，也可以使用 INSERT 更新现有记录。 Ike Walker 有一篇很好的博客文章描述了这一点:How to do an Upsert in Cassandra .