阅读卡桑德拉的失败

Question

我有一个节点cassandra设置。我在cassandra cqlsh上运行select count(*) where查询时遇到以下错误：

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;

回复消息：

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，从该表读取，工作似乎被卡住了。

日志：

在/var/log/cassandra/system.log

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

更多细节：

我可以在同一个表上运行以下查询，没有任何错误：

SELECT * FROM casb.o365_activity_log_by_date;

在查询之上运行我可以看到有些列中大部分都是空值。看到这个和从日志中我猜它与cassandra中的墓碑有关。

我该怎么办？我看着this answer，所以我应该清理墓碑吗？我不确定。

Answer 1

您的查询为Cassandra使用了两种可能的反模式。

首先，您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，因为没有RDBMS中的索引可以快速回答您的问题。请注意SELECT * FROM foo;或SELECT count(*) FROM bar;在Cassandra中总是很慢。

其次，你忽略了Cassandra做出这些事情的警告 - ALLOW FILTERING必须明确写出来。请记住，这是为了保护您完成整个群集读取。您的select语句正在creation_time上过滤，而system.log不是主键的一部分。

所以我敢打赌你的查询运行时会超时。看一下来自Cassandra的/var/log/cassandra/system.log，从包装中安装时经常在qazxswpoi下找到。

一般情况下 - 如果您想使用Cassandra，我建议您浏览一些DataStax提供的数据建模课程。它通常归结为：围绕您将使用的查询构建数据模型 - 必要时进行非规范化，以便理想情况下查询只能访问一个分区键。