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From Inquistive allen <inquial...@gmail.com>
Subject Re: read failures and high read latency
Date Mon, 26 Aug 2019 09:14:43 GMT
Hello Marco,

May you pls share error, exception logs seen in system.log files in the
environment.

Thanks

On Mon, 26 Aug, 2019, 2:40 PM Marco Gasparini, <
marco.gasparini@competitoor.com> wrote:

> hi everybody,
>
> I'm experiencing some read failures and high read latency (watch the
> attached picture for more detailes).
>
> - I have a cluster of 6 nodes with 1.5TB of occupied disk space for each
> node. Running Cassandra 3.11.4
>
> 4 nodes have 32GB of RAM. Cassandra allocations is Xms8G Xmx8G.
> 2 nodes have 16GB of RAM. Cassndra allocations is Xms4G Xmx4G.
>
> Each node has spinning disk.
>
> - Some fields from cassandra.yaml configuration:
>
> concurrent_reads: 64
> concurrent_writes: 64
> concurrent_counter_writes: 64
>
> file_cache_size_in_mb: 2048
>
> memtable_cleanup_threshold: 0.2
> memtable_flush_writers: 4
> memtable_allocation_type: offheap_objects
>
> - CQL schema and RF:
>
> CREATE KEYSPACE myks WITH replication = {'class':
> 'NetworkTopologyStrategy', 'DC1': '3'}  AND durable_writes = false;
> CREATE TABLE myks.mytable (
>     id bigint,
>     type text,
>     page int,
>     event_datetime timestamp,
>     agent text,
>     portion text,
>     raw text,
>     status int,
>     status_code_pass int,
>     dom bigint,
>     reached text,
>     tt text,
>     PRIMARY KEY ((id, type), page, event_datetime)
> ) WITH CLUSTERING ORDER BY (page DESC, event_datetime 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 = 90000
>     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';
>
>
> - I do queries that reads 3 rows at a time where the total data size is
> between 5MB and 20MB.
>
>
> How can I improve the reading performances?
> I could stand losing some writing speed in order to improve the reading
> speed.
>
> if you need more information, please ask.
>
>
> Thanks
> Marco
> [image: grafana_cassandra.png]
>

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