具有相同主键的行插入正在替换Cassandra中的先前写入

Question

在Cassandra中创建了一个表,其中主键基于两列(groupname,type).当我试图在组名和类型相同的情况下插入多于一行时,那么在这种情况下它不会存储多个行,后续写入组名和类型中的相同...那么最新的写入正在替换以前的类似写道.为什么Cassandra会以这种方式替换而不是写入每一行插入？

写1

cqlsh:resto> insert into restmaster (rest_id,type,rname,groupname,address,city,country)values(blobAsUuid(timeuuidAsBlob(now())),'SportsBar','SportsDen','VK Group','Majestic','Bangalore','India');

写2

insert into restmaster (rest_id,type,rname,groupname,address,city,country)values(blobAsUuid(timeuuidAsBlob(now())),'SportsBar','Sports Spot','VK Group','Bandra','Mumbai','India');

写3

cqlsh:resto> insert into restmaster (rest_id,type,rname,groupname,address,city,country)values(blobAsUuid(timeuuidAsBlob(now())),'SportsBar','Cricket Heaven ','VK Group','Connaught Place','New Delhi','India');

我期待的结果(检查第4,5,6行)

 groupname      | type       | rname
----------------+------------+-----------------
           none |      Udipi |  Gayatri Bhavan
           none |     dinein |    Blue Diamond
       VK Group |  FoodCourt |        FoodLion
       VK Group |  SportsBar |      Sports Den
       VK Group |  SportsBar |     Sports Spot
       VK Group |  SportsBar |  Cricket Heaven
  Viceroy Group | Vegetarian |  Palace Heights
 Mainland Group |    Chinese |  MainLand China
      JSP Group |  FoodCourt |        Nautanki
          Ohris |  FoodCourt |           Ohris

但这是实际结果(写3已取代之前的2个插入[第4,5行])

 cqlsh:resto> select groupname,type,rname From restmaster;

 groupname      | type       | rname
----------------+------------+-----------------
           none |      Udipi |  Gayatri Bhavan
           none |     dinein |    Blue Diamond
       VK Group |  FoodCourt |        FoodLion
       VK Group |  SportsBar | Cricket Heaven 
  Viceroy Group | Vegetarian |  Palace Heights
 Mainland Group |    Chinese |  MainLand China
      JSP Group |  FoodCourt |        Nautanki
          Ohris |  FoodCourt |           Ohris


cqlsh:resto> describe table restmaster;

CREATE TABLE restmaster (
  groupname text,
  type text,
  address text,
  city text,
  country text,
  rest_id uuid,
  rname text,
  PRIMARY KEY ((groupname), type)
) 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'};

Answer 1

对Cassandra数据库的所有插入实际上都是插入/更新操作,并且每个唯一定义的主键只能存在一组非键值.这意味着您不能为一个主键提供多组值,并且您只能看到最后一次写入.

更多信息:http: //www.datastax.com/documentation/cql/3.1/cql/cql_intro_c.html

更新:数据模型

如果你使用了像键

Primary Key ((groupname),type,rname)

只要您拥有独特的餐厅名称,您就能获得您期望的结果.但你真正要问的是"我想对这些数据进行哪些查询？" 所有Cassandra表都应该基于满足一类查询.我上面写的关键字基本上说"这个表是为了快速查找特定组中的所有餐馆而构建的,我将使用的唯一条件将是类型和餐馆名称"

您可以使用该架构执行的示例查询

 SELECT * FROM restmaster WHERE groupname = 'Lettuce Entertain You' ;
 SELECT * FROM restmaster WHERE groupname = 'Lettuce Entertain You' and type = 'Formal'  ;
 SELECT * FROM restmaster WHERE groupname = 'Lettuce Entertain You' and type = 'Formal' 
    and rname > 'C' and rname < 'Y' ;

如果这不是您希望在应用程序中执行的查询类型,或者除了这些查询之外还需要其他查询,则很可能需要其他表.