Column Family per User
Our application has users that can write in upwards of 50 million records per day. However, they all write the same format of records (20 fields…columns). Should I put each user in their own column family, even though the column family schema will be the same per user? Would this help with dimensioning, if each user is querying their keyspace and only their keyspace? Trevor Francis
Re: Column Family per User
Each CF takes a fair chunk of memory regardless of how much data it has, so this is probably not a good idea, if you have lots of users. Also using a single CF means that compression is likely to work better (more redundant data). However, Cassandra distributes the load across different nodes based on the row key, and the writes scale roughly linearly according to the number of nodes. So if you can make sure that no single row gets overly burdened by writes (50 million writes/day to a single row would always go to the same nodes - this is in the order of 600 writes/second/node, which shouldn't really pose a problem, IMHO). The main problem is that if a single row gets lots of columns it'll start to slow down at some point, and your row caches become less useful, as they cache the entire row. Keep your rows suitably sized and you should be fine. To partition the data, you can either distribute it to a few CFs based on use or use some other distribution method (like user:1234:00 where the 00 is the hour-of-the-day. (There's a great article by Aaron Morton on how wide rows impact performance at http://thelastpickle.com/2011/07/04/Cassandra-Query-Plans/, but as always, running your own tests to determine the optimal setup is recommended.) /Janne On Apr 18, 2012, at 21:20 , Trevor Francis wrote: Our application has users that can write in upwards of 50 million records per day. However, they all write the same format of records (20 fields…columns). Should I put each user in their own column family, even though the column family schema will be the same per user? Would this help with dimensioning, if each user is querying their keyspace and only their keyspace? Trevor Francis
Re: Column Family per User
Janne, Of course, I am new to the Cassandra world, so it is taking some getting used to understand how everything translates into my MYSQL head. We are building an enterprise application that will ingest log information and provide metrics and trending based upon the data contained in the logs. The application is transactional in nature such that a record will be written to a log and our system will need to query that record and assign two values to it in addition to using the information to develop trending metrics. The logs are being fed into cassandra by Flume. Each of our users will be assigned their own piece of hardware that generates these log events, some of which can peak at up to 2500 transactions per second for a couple of hours. The log entries are around 150-bytes each and contain around 20 different pieces of information. Neither us, nor our users are interested in generating any queries across the entire database. Users are only concerned with the data that their particular piece of hardware generates. Should I just setup a single column family with 20 columns, the first of which being the row key and make the row key the username of that user? We would also need probably 2 more columns to store Value A and Value B assigned to that particular record. Our metrics will be be something like this: For this particular user, during this particular timeframe, what is the average of field X? And then store that value, which we can generate historical trending over the course a week. We will do this every 15 minutes. Any suggestions on where I should head to start my journey into Cassandra for my particular application? Trevor Francis On Apr 18, 2012, at 2:14 PM, Janne Jalkanen wrote: Each CF takes a fair chunk of memory regardless of how much data it has, so this is probably not a good idea, if you have lots of users. Also using a single CF means that compression is likely to work better (more redundant data). However, Cassandra distributes the load across different nodes based on the row key, and the writes scale roughly linearly according to the number of nodes. So if you can make sure that no single row gets overly burdened by writes (50 million writes/day to a single row would always go to the same nodes - this is in the order of 600 writes/second/node, which shouldn't really pose a problem, IMHO). The main problem is that if a single row gets lots of columns it'll start to slow down at some point, and your row caches become less useful, as they cache the entire row. Keep your rows suitably sized and you should be fine. To partition the data, you can either distribute it to a few CFs based on use or use some other distribution method (like user:1234:00 where the 00 is the hour-of-the-day. (There's a great article by Aaron Morton on how wide rows impact performance at http://thelastpickle.com/2011/07/04/Cassandra-Query-Plans/, but as always, running your own tests to determine the optimal setup is recommended.) /Janne On Apr 18, 2012, at 21:20 , Trevor Francis wrote: Our application has users that can write in upwards of 50 million records per day. However, they all write the same format of records (20 fields…columns). Should I put each user in their own column family, even though the column family schema will be the same per user? Would this help with dimensioning, if each user is querying their keyspace and only their keyspace? Trevor Francis
Re: Column Family per User
Your design should be around how you want to query. If you are only querying by user, then having a user as part of the row key makes sense. To manage row size, you should think of a row as being a bucket of time. Cassandra supports a large (but not without bounds) row size. To manage row size you might say that this row is for user fred for the month of april, or if that's too much perhaps the row is for user fred for the day 4/18/12. To do this you can use composite keys to hold both pieces of information in the key. (user, bucketpos)The nice thing is that once the time period has come and gone, that row is complete, and you can perform background jobs against that row and store summary information for that time period. - Original Message -From: quot;Trevor Francisquot; ;trevor.fran...@tgrahamcapital.com
Re: Column Family per User
I am trying to grasp this concept….so let me try a scenario. Lets say I have 5 data points being captured in the log file. Here would be a typical table schema in mysql. Id, Username, Time, Wind, Rain, Sunshine Select * from table; would reveal: 1, george, 2012-04-12T12:22:23.293, 55, 45, 10 2, george, 2012-04-12T12:22:24.293, 45, 25, 25 3, george, 2012-04-12T12:22:25.293, 35, 15, 11 4, george, 2012-04-12T12:22:26.293, 55, 65, 16 5, george, 2012-04-12T12:22:27.293, 12, 5, 22 And it would just continue from there adding rows as log files are imported. A select * from table where sunshine=16 would yield: 4, george, 2012-04-12T12:22:26.293, 55, 65, 16 Now, you are saying that in Cassandra, Instead of having a bunch of rows containing ordered information (which is what I would have), I would have a single row with multiple columns: George | 2012-04-12T12:22:23.293, wind=55 | 2012-04-12T12:22:23.293, Rain=45 | 2012-04-12T12:22:23.293, Sunshine=10 | .continued. So George would be the row and the columns would be the actual data. The data would be oriented horizontally, vs vertically (mysql). So for instance, log generation on our application isn't linear as it peaks at certain times of the day. A user generating at peak 2500 would typically generate 60M log entries per day. Multiply that times 20 data pieces and you are looking at 1.2B Columns in a given day for that user. Assuming we batches the writes every minute, can a node handle this sort of load? Also, can we rotate the row every day? Would it make more sense to rotate hourly? At peak, hourly rotation would decrease the row size to 180M data points vs. 1.2B. At max, we may only have 500 users on our platform. That means that if we did hourly row rotation, that would be 12,000 rows per day…with the maximum column size of 180M columns. Am I grasping this concept properly? Trevor Francis On Apr 18, 2012, at 3:06 PM, Dave Brosius wrote: Your design should be around how you want to query. If you are only querying by user, then having a user as part of the row key makes sense. To manage row size, you should think of a row as being a bucket of time. Cassandra supports a large (but not without bounds) row size. To manage row size you might say that this row is for user fred for the month of april, or if that's too much perhaps the row is for user fred for the day 4/18/12. To do this you can use composite keys to hold both pieces of information in the key. (user, bucketpos) The nice thing is that once the time period ha s come and gone, that row is complete, and you can perform background jobs against that row and store summary information for that time period. - Original Message - From: Trevor Francis trevor.fran...@tgrahamcapital.com Sent: Wed, April 18, 2012 15:48 Subject: Re: Column Family per User Janne, Of course, I am new to the Cassandra world, so it is taking some getting used to understand how everything translates into my MYSQL head. We are building an enterprise application that will ingest log inf ormation and provide metrics and trending based upon the data contained in the logs. The application is transactional in nature such that a record will be written to a log and our system will need to query that record and assign two values to it in addition to using the information to develop trending metrics. The logs are being fed into cassandra by Flume. Each of our users will be assigned their own piece of hardware that generates these log events, some of which can peak at up to 2500 transactions per second for a couple of hours. The log entries are around 150-bytes each and contain around 20 different pieces of information. Neither us, nor our users are interested in generating any queries across the entire database. Users are only concerned with the data that their particular piece of hardware generates. Should I just setup a single column family with 20 columns, the first of which bei ng the row key and make the row key the username of that user? We would also need probably 2 more columns to store Value A and Value B assigned to that particular record. Our metrics will be be something like this: For this particular user, during this particular timeframe, what is the average of field X? And then store that value, which we can generate historical trending over the course a week. We will do this every 15 minutes. Any suggestions on where I should head to start my journey into Cassandra for my particular application? Trevor Francis On Apr 18, 2012, at 2:14 PM, Janne Jalkanen wrote: Each CF takes a fair chunk of memory regardless of how much data it has, so this is probably not a good idea, if you have lots of users. Also using a single CF means that compression is likely to work better (more redundant data). However, Cassandra distributes the load across different nodes
Re: Column Family per User
Yes in this cassandra model, time wouldn't be a column value, it would be part of the column name. Depending on how you want to access your data (give me all data points for time X) and how many separate datapoints you have for time X, you might consider packing all the data for a time in one column thru composite columnscolumn name: 2012-04-12T12:22:23.293/55/45/10 (where / is a human readable representation of the composite separator) in this case there wouldn't actually be a value, the data is just encoded in the column name.Obviously if you are storing dozens of separate datapoints for a timestamp than this gets out of hand quickly, and perhaps you need to go back to column names with time/fieldname format with a real value.the advantage tho of the composite key is that you eliminate all that constant blather about 'Wind' 'Rain' 'Sunshine' in your data and only hold real data. (granted compression will probably help here, but not having it all is even better).as for row size, obv iously that takes some experimentation on you part. You can bucket a row to be any time frame you want. If you feel that 15 minutes is the correct length of time given the amount of data you will write, then use 15 minutes. It it's 1 hour, use 1 hour. The only thing you have to figure out is a 'bucket time' definition that you understand, likely it's the timestamp of when that time period starts.As for 'rotating the row', perhaps it's just semantics, but there really is no such concept. You are at some point in time, and you want to write some data to the database.The steps are1) get the user2) get the timestamp of the current bucket based on 'now'3) build a composite key4) insert the data with that keyWhether that row existed before or is a new row has no bearing on your client code. - Original Message -From: quot;Trevor Francisquot; ;trevor.fran...@tgrahamcapital.com
Re: Column Family per User
Yes in this cassandra model, time wouldn't be a column value, it would be part of the column name. Depending on how you want to access your data (give me all data points for time X) and how many separate datapoints you have for time X, you might consider packing all the data for a time in one column thru composite columnscolumn name: 2012-04-12T12:22:23.293/55/45/10 (where / is a human readable representation of the composite separator) in this case there wouldn't actually be a value, the data is just encoded in the column name.Obviously if you are storing dozens of separate datapoints for a timestamp than this gets out of hand quickly, and perhaps you need to go back to column names with time/fieldname format with a real value.the advantage tho of the composite key is that you eliminate all that constant blather about 'Wind' 'Rain' 'Sunshine' in your data and only hold real data. (granted compression will probably help here, but not having it all is even better).as for row size, obviously that takes some experimentation on you part. You can bucket a row to be any time frame you want. If you feel that 15 minutes is the correct length of time given the amount of data you will write, then use 15 minutes. It it's 1 hour, use 1 hour. The only thing you have to figure out is a 'bucket time' definition that you understand, likely it's the timestamp of when that time period starts.As for 'rotating the row', perhaps it's just semantics, but there really is no such concept. You are at some point in time, and you want to write some data to the database.The steps are1) get the user2) get the timestamp of the current bucket based on 'now'3) build a composite key4) insert the data with that keyWhether that row existed before or is a new row has no bearing on your client code. - Original Message -From: quot;Trevor Francisquot; ;trevor.fran...@tgrahamcapital.com;trevor.fran...@tgrahamcapital.com
Re: Column Family per User
Regarding Rotating, I was thinking about the concept of log rotate, where you
write to a file for a specific period of time, then you create a new file and
write to it after a specific set of time. So yes, it closes a row and opens
another row.
Since I will be generating analytics every 15 minutes, its would make sense to
me to bucket a row every 15 minutes. Since I would only have at most 500 users,
this doesn't strike me as too many rows in a given day (48,000). Potential
downsides to doing this?
Since I am analyzing 20 separate data points for a given log entry, it would
make sense that querying based upon a specific metric (wind, rain, sunshine)
would be easier if the data was separated. However, couldn't we build composite
columns for time and value where all that would be left in data?
So composite row key would be:
george
2012-04-12T12:20
And Columns would be:
12:22:23.293/Wind
12:22:23.293/Rain
12:22:23.293/Sunshine
Data would be:
55
45
10
Our the columns could be 12:22:23.293
Data:
Wind/55/45/35
Or something like that….Am I headed in the right direction?
Trevor Francis
On Apr 18, 2012, at 3:10 PM, Janne Jalkanen wrote:
Hi!
A simple model to do this would be
* ColumnFamily Data
* key: userid
* column: Composite( timestamp, entrytype ) = value
For example, userid janne would have columns
(2012-04-12T12:22:23.293,speed) = 24;
(2012-04-12T12:22:23.293,temperature) = 12.4
(2012-04-12T12:22:23.293,direction) = 356;
(2012-04-12T12:22:23.295,speed) = 24.1;
(2012-04-12T12:22:23.295,temperature) = 12.3
(2012-04-12T12:22:23.295,direction) = 352;
Note that Cassandra does not require you to know which columns you're going
to put in it (unlike MySQL). You can declare types ahead if you know what
they are, but if you'll need to start adding a new column, just start writing
it and Cassandra should do the right things.
However, there are a few points which you might want to consider
* Using ISO dates for timestamps have a minor problem: if two events occur
during the same millisecond, they'll overwrite each other. This is why most
time series in C* use TimeUUIDs, which contain a millisecond timestamp + a
random component.
(http://rubyscale.com/blog/2011/03/06/basic-time-series-with-cassandra/)
* This will generate timestamp*entrytype columns. So for 2500 entries/second
and 20 columns this means about 2500*20 = 5 wps (granted that you will
most probably batch the writes though). You will need to performance test
your cluster to see if this schema is right for you. If not, you might want
to try and see how you can distribute the keys differently, e.g. by bucketing
the data somehow. However, I recommend that you build a first-shot of your
app structure, then load test it until it breaks and that should give you
pretty good understanding of what exactly cassandra is doing.
To do then analytics multiple options are possible; a popular one is to run
MapReduce queries using a tool like Apache Pig on regular intervals. DataStax
has good documentation and you probably want to take a look at their offering
as well, since they have pretty good Hadoop/MapReduce support for Cassandra.
CLI syntax to try with:
create keyspace DataTest with
placement_strategy='org.apache.cassandra.locator.SimpleStrategy' and
strategy_options = {replication_factor:1};
use DataTest;
create column family Data with key_validation_class=UTF8Type and
comparator='CompositeType(UUIDType,UTF8Type)';
Then start writing using your fav client.
/Janne
On Apr 18, 2012, at 22:36 , Trevor Francis wrote:
Janne,
Of course, I am new to the Cassandra world, so it is taking some getting
used to understand how everything translates into my MYSQL head.
We are building an enterprise application that will ingest log information
and provide metrics and trending based upon the data contained in the logs.
The application is transactional in nature such that a record will be
written to a log and our system will need to query that record and assign
two values to it in addition to using the information to develop trending
metrics.
The logs are being fed into cassandra by Flume.
Each of our users will be assigned their own piece of hardware that
generates these log events, some of which can peak at up to 2500
transactions per second for a couple of hours. The log entries are around
150-bytes each and contain around 20 different pieces of information.
Neither us, nor our users are interested in generating any queries across
the entire database. Users are only concerned with the data that their
particular piece of hardware generates.
Should I just setup a single column family with 20 columns, the first of
which being the row key and make the row key the username of that user?
We would also need probably 2 more columns to store Value A and Value B
assigned to that particular record.
Re: Column Family per User
It seems to me you are on the right track. Finding the right balance of # rows vs row width is the part that will take the most experimentation. - Original Message -From: quot;Trevor Francisquot; ;trevor.fran...@tgrahamcapital.com
