Thank you for that. I did not have trickle_fsync enabled and will give it a
try. I just noticed that when running a describe on my table, I do not see the
sstable size parameter (compaction_strategy_options = {'sstable_size_in_mb':5})
included. Is that expected? Does it mean its using the defaults?
Assuming none of the tuning here makes a noticeable difference, my next step is
to try switching from LZ4 to Snappy. Any opinions on that?
Thanks!
CREATE TABLE global_user (
user_id bigint,
app_id int,
type text,
name text,
extra_param map<text, text>,
last timestamp,
paid boolean,
sku_time map<text, timestamp>,
values map<timestamp, float>,
PRIMARY KEY (user_id, app_id, type, name)
) WITH
bloom_filter_fp_chance=0.100000 AND
caching='KEYS_ONLY' AND
comment='' AND
dclocal_read_repair_chance=0.000000 AND
gc_grace_seconds=86400 AND
read_repair_chance=0.100000 AND
replicate_on_write='true' AND
populate_io_cache_on_flush='false' AND
compaction={'class': 'LeveledCompactionStrategy'} AND
compression={'chunk_length_kb': '8', 'crc_check_chance': '0.1',
'sstable_compression': 'LZ4Compressor'};
From: Igor <[email protected]<mailto:[email protected]>>
Reply-To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Date: Thursday, May 16, 2013 4:27 PM
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: Re: SSTable size versus read performance
just in case it will be useful to somebody - here is my checklist for better
read performance from SSD
1. limit read-ahead to 16 or 32
2. enable 'trickle_fsync' (available starting from cassandra 1.1.x)
3. use 'deadline' io-scheduler (much more important for rotational drives then
for SSD)
4. format data partition starting on 2048 sector boundary
5. use ext4 with noatime,nodiratime,discard mount options
On 05/16/2013 10:48 PM, Edward Capriolo wrote:
I was going to say something similar I feel like the SSD drives read much
"more" then the standard drive. Read Ahead/arge sectors could and probably does
explain it.
On Thu, May 16, 2013 at 3:43 PM, Bryan Talbot
<[email protected]<mailto:[email protected]>> wrote:
512 sectors for read-ahead. Are your new fancy SSD drives using large sectors?
If your read-ahead is really reading 512 x 4KB per random IO, then that 2 MB
per read seems like a lot of extra overhead.
-Bryan
On Thu, May 16, 2013 at 12:35 PM, Keith Wright
<[email protected]<mailto:[email protected]>> wrote:
We actually have it set to 512. I have tried decreasing my SSTable size to 5
MB and changing the chunk size to 8 kb
From: Igor <[email protected]<mailto:[email protected]>>
Reply-To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Date: Thursday, May 16, 2013 1:55 PM
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: Re: SSTable size versus read performance
My 5 cents: I'd check blockdev --getra for data drives - too high values for
readahead (default to 256 for debian) can hurt read performance.
