Cassandra 支持哪些类型的墓碑？

Question

Cassandra（第 2 版）支持哪些类型的墓碑？根据this它支持的文章（以CQL术语）：

• 一行的特定列。
• 静态列。
• 分区键的所有行。

我是否遗漏了其他类型的墓碑？删除特定（CQL）行？是否有任何特殊的墓碑来支持删除集群键或类似的范围？在规划模式以避免过多的墓碑时，了解此信息很有用。

Answer 1

墓碑是放置在指示删除的行中的标记。它们可以存在于不同的位置、列或列的范围内，或者整行。下面的例子展示了普通类型的墓碑（范围类型这里不涉及）。

在规划架构时，您根据正在执行的查询类型对表进行建模，而不是使用一张表，您可能会发现数据在许多表中重复。这些表经过优化以服务传入的读取和写入。下面的链接应该为您提供有关使用 Cassandra 进行数据建模的一些良好背景：

http://www.datastax.com/resources/data-modeling

我的例子：我创建了一个表并插入了一些数据，然后使用nodetool flush 生成了一些 sstables。使用sstable2json 工具，您可以看到已删除的行，如果它是一整行，它看起来与单列略有不同，但本质上它仍然只是一个标记：

这是包含所有数据的表格：

$ ~/dse-4.5.1/resources/cassandra/bin/sstable2json ./dse-data/results/ts1/results-ts1-jb-1-Data.db 
[
{"key": "3136","columns": [["","",1417814256390000], ["col2","26",1417814256390000], ["col3","36",1417814256390000], ["id","id16",1417814256390000]]},
{"key": "3133","columns": [["","",1417814218246000], ["col2","23",1417814218246000], ["col3","33",1417814218246000], ["id","id13",1417814218246000]]},
{"key": "3135","columns": [["","",1417814244766000], ["col2","25",1417814244766000], ["col3","35",1417814244766000], ["id","id15",1417814244766000]]},
{"key": "3134","columns": [["","",1417814230711000], ["col2","24",1417814230711000], ["col3","34",1417814230711000], ["id","id14",1417814230711000]]},
{"key": "3132","columns": [["","",1417814207910000], ["col2","22",1417814207910000], ["col3","32",1417814207910000], ["id","id12",1417814207910000]]},
{"key": "3131","columns": [["","",1417814197094000], ["col2","21",1417814197094000], ["col3","31",1417814197094000], ["id","id11",1417814197094000]]},
{"key": "31","columns": [["","",1417814185270000], ["col2","2",1417814185270000], ["col3","3",1417814185270000], ["id","id1",1417814185270000]]}
]

这是cqlsh中的第一个删除：

cqlsh:results> delete from ts1 WHERE col1 = '1';
cqlsh:results> delete id from ts1 WHERE col1 = '11';

这是刷新后的结果 sstable：

[datastax@DSE3 ~]$ ~/dse-4.5.1/resources/cassandra/bin/sstable2json ./dse-data/results/ts1/results-ts1-jb-2-Data.db 
[
{"key": "3131","columns": [["id","54822130",1417814320400000,"d"]]},
{"key": "31","metadata": {"deletionInfo": {"markedForDeleteAt":1417814302304000,"localDeletionTime":1417814302}},"columns": []}
]

这是 cqlsh 中的下一个删除：

cqlsh:results> delete col2 from ts1 WHERE col1 = '12';

这是刷新后的结果 sstable：

[datastax@DSE3 ~]$ ~/dse-4.5.1/resources/cassandra/bin/sstable2json ./dse-data/results/ts1/results-ts1-jb-3-Data.db 
[
{"key": "3132","columns": [["col2","5482220b",1417814539434000,"d"]]}
]

当压缩发生时，所有这些 sstable 被合并到一个 sstable 中，然后删除的行仍然存在，但标记为删除，我们可以在运行压缩后再次看到这一点（查找带有时间戳的 d 标志） ：

[datastax@DSE3 ~]$ ./dse-4.5.1/bin/nodetool compact
[datastax@DSE3 ~]$ ~/dse-4.5.1/resources/cassandra/bin/sstable2json ./dse-data/results/ts1/results-ts1-jb-4-Data.db 
[
{"key": "3136","columns": [["","",1417814256390000], ["col2","26",1417814256390000], ["col3","36",1417814256390000], ["id","id16",1417814256390000]]},
{"key": "3133","columns": [["","",1417814218246000], ["col2","23",1417814218246000], ["col3","33",1417814218246000], ["id","id13",1417814218246000]]},
{"key": "3135","columns": [["","",1417814244766000], ["col2","25",1417814244766000], ["col3","35",1417814244766000], ["id","id15",1417814244766000]]},
{"key": "3134","columns": [["","",1417814230711000], ["col2","24",1417814230711000], ["col3","34",1417814230711000], ["id","id14",1417814230711000]]},
{"key": "3132","columns": [["","",1417814207910000], ["col2","5482220b",1417814539434000,"d"], ["col3","32",1417814207910000], ["id","id12",1417814207910000]]},
{"key": "3131","columns": [["","",1417814197094000], ["col2","21",1417814197094000], ["col3","31",1417814197094000], ["id","54822130",1417814320400000,"d"]]},
{"key": "31","metadata": {"deletionInfo": {"markedForDeleteAt":1417814302304000,"localDeletionTime":1417814302}},"columns": []}
]

现在这个表将保持这种状态，直到我们到达 gc_grace_seconds，然后在下一次压缩时，行实际上会消失，注意我们删除 gc_grace_seconds 然后运行压缩：

cqlsh> ALTER TABLE results.ts1 WITH gc_grace_seconds=500;
cqlsh> exit
[datastax@DSE3 ~]$ ./dse-4.5.1/bin/nodetool compact results;

[datastax@DSE3 ~]$ ./dse-4.5.1/resources/cassandra/bin/sstable2json ./dse-data/results/ts1/results-ts1-jb-5-Data.db 
[
{"key": "3136","columns": [["","",1417814256390000], ["col2","26",1417814256390000], ["col3","36",1417814256390000], ["id","id16",1417814256390000]]},
{"key": "3133","columns": [["","",1417814218246000], ["col2","23",1417814218246000], ["col3","33",1417814218246000], ["id","id13",1417814218246000]]},
{"key": "3135","columns": [["","",1417814244766000], ["col2","25",1417814244766000], ["col3","35",1417814244766000], ["id","id15",1417814244766000]]},
{"key": "3134","columns": [["","",1417814230711000], ["col2","24",1417814230711000], ["col3","34",1417814230711000], ["id","id14",1417814230711000]]},
{"key": "3132","columns": [["","",1417814207910000], ["col3","32",1417814207910000], ["id","id12",1417814207910000]]},
{"key": "3131","columns": [["","",1417814197094000], ["col2","21",1417814197094000], ["col3","31",1417814197094000]]}
]

请注意键 31 的行以及键 3132 的行中的 col1 和键 3131 的行中的 id

为了清楚起见，我的表架构：

cqlsh:results> DESCRIBE TABLE ts1 ;

CREATE TABLE ts1 (
  col1 text,
  col2 text,
  col3 text,
  id text,
  PRIMARY KEY ((col1))
) 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'};

作为脚注，sstable2json 输出中的墓碑标记如下：

e - 过期的 TTL

d - 删除值（墓碑）

t - 删除的值范围（范围墓碑）

Answer 2

除了@markc 的答案之外，还有一个列范围墓碑，每当您使用集合时都会显示。我们有一个名为“tags”的set<text> 列，每当我们插入一行时，我们都会得到其中的一个（即使我们只是将它设置为 null，就像在本例中一样）：

["1381316637599609:45787829:tags:_","1381316637599609:45787829:tags:!",1438264650252000,"t",1438264650],

我们认为“t”代表墓碑。 This blog post 详细介绍了这种墓碑的另一个例子。