Greetings, We have recently introduced Cassandra at the Globe and Mail here in Toronto, Canada. We are processing and storing the North American stock-market feed. We have found it to work very quickly and things have been looking very good.
Recently we upgraded to version 1.1.1 and then we have noticed some issues
occurring.
I will try to describe it for you here. Basically one operation that we very
often perform and is very critical is the ability to 'get the latest quote'.
This would return to you the latest Quote adjusted against exchange delay
rules. With Cassandra version 1.0.3 we could get a Quote in around 2ms. After
update we are looking at time of at least 2-3 seconds.
The way we query the quote is using a REVERSED SuperSliceQuery with start=now,
end=00:00:00.000 (beginning of day) LIMITED to 1.
Our investigation leads us to suspect that, since upgrade, Cassandra seems to
be reading the sstable from disk even when we request a small range of day only
5 seconds back. If you look at the output below you can see that the query
does NOT get slower as the lookback increases from 5 sec, 60 sec, 15 min, 60
min, and 24 hours.
We also noticed that the query was very fast for the first five minutes of
trading, apparently until the first sstable was flushed to disk. After that we
go into query times of 1-2 seconds or so.
Query time[lookback=5]:[1711ms]
Query time[lookback=60]:[1592ms]
Query time[lookback=900]:[1520ms]
Query time[lookback=3600]:[1294ms]
Query time[lookback=86400]:[1391ms]
We would really appreciate input or help on this.
Cassandra version: 1.1.1
Hector version: 1.0-1
---
public void testCassandraIssue() {
try {
int[] seconds = new int[]{ 5, 60, 60 * 15, 60 * 60, 60 * 60 *
24};
for(int sec : seconds) {
DateTime start = new DateTime();
SuperSliceQuery<String, String, String, String>
superSliceQuery = HFactory.createSuperSliceQuery(keyspaceOperator,
StringSerializer.get(), StringSerializer.get(), StringSerializer.get(),
StringSerializer.get());
superSliceQuery.setKey("101390" + "." +
testFormatter.print(start));
superSliceQuery.setColumnFamily("Quotes");
superSliceQuery.setRange(superKeyFormatter.print(start),
superKeyFormatter.print(start.minusSeconds(sec)),
true,
1);
long theStart = System.currentTimeMillis();
QueryResult<SuperSlice<String, String, String>> result
= superSliceQuery.execute();
long end = System.currentTimeMillis();
System.out.println("Query time[lookback=" + sec + "]:["
+ (end - theStart) + "ms]");
}
} catch(Exception e) {
e.printStackTrace();
fail(e.getMessage());
}
}
---
create column family Quotes
with column_type = Super
and comparator = BytesType
and subcomparator = BytesType
and keys_cached = 7000
and rows_cached = 0
and row_cache_save_period = 0
and key_cache_save_period = 3600
and memtable_throughput = 255
and memtable_operations = 0.29
AND compression_options={sstable_compression:SnappyCompressor,
chunk_length_kb:64};
-Ivan/
---
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Ivan Ganza | Senior Developer | Information Technology
c: 647.701.6084 | e: iga...@globeandmail.com
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