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From John Belliveau <>
Subject RE: Constant blocking read repair for such a tiny table
Date Thu, 03 Oct 2019 21:21:24 GMT
Hi Patrick,

Is this time series data? If so, I have run into issues with repair on time series data using
the SizeTieredCompactionStrategy. I have had better luck using the TimeWindowCompactionStrategy.


Sent from Mail for Windows 10

From: Patrick Lee
Sent: Thursday, October 3, 2019 5:14 PM
Subject: Constant blocking read repair for such a tiny table

I have a cluster that is running 3.11.4 ( was upgraded a while back from 2.1.16 ).  what
I see is a steady rate of read repair which is about 10% constantly on only this 1 table. 
Repairs have been run (actually several times).  The table does not have a lot of writes
to it so after repair, or even after a read repair I would expect it to be fine.  the reason
i'm having to dig into this so much is for the fact that under a much large traffic load than
their normal traffic, latencies are higher than the app team wants

I mean this thing is tiny, it's a 12x12 cluster but this 1 table is like 1GB per node on disk.

the application team is doing reads at LOCAL_QUORUM and I can simulate this on that cluster
by running a query using quorum and/or local_quorum and in the trace can see every time running
the query it comes back with a DigestMismatchException no matter how many times I run it.
that record hasn't been updated by the application for several months.

repairs are scheduled and run every 7 days via reaper, recently in the past week this table
has been repaired at least 3 times.  every time there are mismatches and data streams back
and forth but yet still a constant rate of read repairs. 

curious if anyone has any recommendations to look info further or have experienced anything
like this?

this node has been up for 24 hours.. this is the netstats for read repairs
Not sending any streams.
Read Repair Statistics:
Attempted: 7481
Mismatch (Blocking): 11425375
Mismatch (Background): 17
Pool Name                    Active   Pending      Completed   Dropped
Large messages                  n/a         0           1232        
Small messages                  n/a         0      395903678         0
Gossip messages                 n/a         0         603746         0

example of the schema... some modifications have been made to reduce read_reapair and speculative_retry
while troubleshooting.. 
CREATE TABLE keyspace.table1 (
    item bigint,
    price int,
    start_date timestamp,
    end_date timestamp,
    created_date timestamp,
    cost decimal,
    list decimal,
    item_id int,
    modified_date timestamp,
    status int,
    PRIMARY KEY ((item, price), start_date, end_date)
) WITH CLUSTERING ORDER BY (start_date ASC, end_date ASC)
    AND read_repair_chance = 0.0
    AND dclocal_read_repair_chance = 0.0
    AND gc_grace_seconds = 864000
    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' : 4, 'class' : ''
    AND default_time_to_live = 0
    AND speculative_retry = 'NONE'
    AND min_index_interval = 128
    AND max_index_interval = 2048
    AND crc_check_chance = 1.0
    AND cdc = false
    AND memtable_flush_period_in_ms = 0;

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