读“卡桑德拉”的失败

Question

我有一个单节点卡桑德拉设置。在对表运行select count(*) where查询时，在cassandra中得到以下错误：

完整查询：

SELECT count(*) FROM casb.o365_activity_log_by_date WHERE
creation_time > '2018-09-16 00:00:00' and creation_time < '2018-09-16 23:59:59' 
ALLOW FILTERING;

响应消息：

ReadFailure: Error from server: code=1300 [Replica(s) failed to execute read] 
message="Operation failed - received 0 responses and 1 failures" 
info={'failures': 1, 'received_responses': 0, 'required_responses': 1, 'consistency': 'ONE'}

表模式：

CREATE TABLE IF NOT EXISTS casb.o365_activity_log_by_date (
    current_date date,
    creation_time timestamp,
    insertion_time timestamp,
    id text,
    client_ip text,
    workload text,
    operation text,
    user_id text,
    object_id text,
    activity_detail text,
    PRIMARY KEY ((current_date), insertion_time, id)
    )
) WITH CLUSTERING ORDER BY (insertion_time DESC, id DESC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99PERCENTILE';

我有另一个基于python的应用程序，它是从那个表中读取的，而且任务似乎被卡住了。

日志：

在/var/log/cassandra/system.log中

WARN  [ReadStage-2] 2018-09-16 22:06:48,803 ReadCommand.java:533 - Read 58545 live rows and 100001 tombstone cells for query SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-16 00:00Z AND creation_time < 2018-09-16 23:59Z LIMIT 100 (see tombstone_warn_threshold)
ERROR [ReadStage-2] 2018-09-16 22:06:48,804 StorageProxy.java:1906 - Scanned over 100001 tombstones during query 'SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-16 00:00Z AND creation_time < 2018-09-16 23:59Z LIMIT 100' (last scanned row partion key was ((2018-09-15), 2018-09-15 08:09Z, 72160ee4-5310-4941-af92-d27ced9c9ca8)); query aborted
WARN  [Native-Transport-Requests-1] 2018-09-16 22:07:02,937 SelectStatement.java:430 - Aggregation query used without partition key
WARN  [Native-Transport-Requests-1] 2018-09-16 22:07:45,946 SelectStatement.java:430 - Aggregation query used without partition key
WARN  [ReadStage-2] 2018-09-16 22:07:47,200 ReadCommand.java:533 - Read 58545 live rows and 100001 tombstone cells for query SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-16 00:00Z AND creation_time < 2018-09-16 23:59Z LIMIT 100 (see tombstone_warn_threshold)
ERROR [ReadStage-2] 2018-09-16 22:07:47,200 StorageProxy.java:1906 - Scanned over 100001 tombstones during query 'SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-16 00:00Z AND creation_time < 2018-09-16 23:59Z LIMIT 100' (last scanned row partion key was ((2018-09-15), 2018-09-15 08:09Z, 72160ee4-5310-4941-af92-d27ced9c9ca8)); query aborted
WARN  [Native-Transport-Requests-1] 2018-09-16 22:17:52,810 SelectStatement.java:430 - Aggregation query used without partition key
WARN  [ReadStage-2] 2018-09-16 22:17:54,513 ReadCommand.java:533 - Read 58545 live rows and 100001 tombstone cells for query SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-17 00:00Z AND creation_time < 2018-09-17 23:59Z LIMIT 100 (see tombstone_warn_threshold)
ERROR [ReadStage-2] 2018-09-16 22:17:54,513 StorageProxy.java:1906 - Scanned over 100001 tombstones during query 'SELECT * FROM casb.o365_activity_log_by_date WHERE creation_time > 2018-09-17 00:00Z AND creation_time < 2018-09-17 23:59Z LIMIT 100' (last scanned row partion key was ((2018-09-15), 2018-09-15 08:09Z, 72160ee4-5310-4941-af92-d27ced9c9ca8)); query aborted
WARN  [Native-Transport-Requests-3] 2018-09-16 22:18:09,541 SelectStatement.java:430 - Aggregation query used without partition key
INFO  [ScheduledTasks:1] 2018-09-16 22:18:17,143 NoSpamLogger.java:91 - Some operations were slow, details available at debug level (debug.log)
WARN  [Native-Transport-Requests-1] 2018-09-16 22:18:28,160 SelectStatement.java:430 - Aggregation query used without partition key
WARN  [Native-Transport-Requests-1] 2018-09-16 22:18:47,943 SelectStatement.java:430 - Aggregation query used without partition key
INFO  [CompactionExecutor:75] 2018-09-16 22:28:26,738 AutoSavingCache.java:394 - Saved KeyCache (48 items) in 250 ms
INFO  [IndexSummaryManager:1] 2018-09-16 22:29:27,992 IndexSummaryRedistribution.java:75 - Redistributing index summaries

详细信息：

我可以在同一个表上运行以下查询，不会出现任何错误：

SELECT * FROM casb.o365_activity_log_by_date;

在上面的查询中，我可以看到有些列的值大多为空。看到这个，从原木上看，我猜这和卡桑德拉的墓碑有关。

我在这里该怎么办？我查看了this answer，所以我应该清理墓碑吗？我不确定。

Answer 1

您的查询对Cassandra使用了两种可能的反模式。

首先，您正在尝试计算整个数据库中的所有键。这将导致在Cassandra中读取磁盘上的所有数据，因为在RDBMS中没有索引可以快速回答您的问题。要警惕的是，SELECT * FROM foo;或SELECT count(*) FROM bar;在卡桑德拉总是很慢。

其次，您忽略了Cassandra发出的警告，即必须显式地编写ALLOW FILTERING。请记住，这是为了保护您完成整个集群读取。select语句在creation_time上筛选，这不是主键的一部分。

因此，我敢打赌，当查询运行时，您将执行超时操作。查看您来自Cassandra的system.log，通常在从软件包安装时在/var/log/cassandra/system.log下找到。

一般来说，如果您想使用Cassandra，我建议您学习一些数据建模课程，例如，可以从DataStax获得。它通常归结为:围绕您将要使用的查询构建数据模型--如果需要的话-去denormalize，以便您的查询理想情况下只按一个分区键。