Tuning and Performance of Bullet in Storm

The performance of a Bullet instance running on a multi-tenant Storm cluster has a lot of independent variables that we could vary and have an effect including:

  1. The amount of data we consume
  2. The number of simultaneous queries Bullet runs
  3. The kinds of simultaneous queries - RAW, GROUP, COUNT DISTINCT, etc.
  4. Varying parallelisms of the components - increase the parallelisms of Filter bolts disproportionately to others
  5. The hardware configuration of machines
  6. The various Storm versions
  7. How free the cluster is and the kinds of topologies running on the cluster - CPU heavy, Disk/memory heavy, network heavy etc
  8. The source of the data and tuning consumption from it

...and many more.

As a streaming system, the two main features to measure is how much data it operates on and how many queries can you run simultaneously (1 and 2 above). For these results, see [performance][../performance.md]. This section will deal with determining what these are and how they vary. We will focus on 1 and 2, while keeping the others as fixed as possible. This section is to give you some insight as to what to tune to improve performance. This is not meant to be a rigorous benchmark.

Prerequisites

You should be familiar with Storm, Kafka and the Bullet on Storm architecture.

How was this tested?

All tests run here were using Bullet-Storm 0.4.2 and Bullet-Storm 0.4.3. We are working with just the Storm piece without going through the Web Service or the UI. The DRPC REST endpoint provided by Storm lets us do just that.

This particular version of Bullet on Storm was prior to the architecture shift to a PubSub layer but this would be the equivalent to using the Storm DRPC PubSub layer on a newer version of Bullet on Storm. You can replace DRPC spout and PrepareRequest bolt with Query spout and ReturnResults bolt with Result bolt conceptually. The actual implementation of the DRPC based PubSub layer just uses these spout and bolt implementations underneath anyway for the Publishers and Subscribers so the parallelisms and CPU utilizations should map 1-1.

Using the pluggable metrics interface in Bullet on Storm, we captured worker level metrics such as CPU time, Heap usage, GC times and types, sent them to a in-house monitoring service for time-slicing and graphing. The figures shown below use this service.

See 0.3.0 for how to plug in your own metrics collection.

Old Version of Bullet

This was tested with a relatively old version of Bullet Storm and has not been updated since. With the latest changes in Storm, Bullet Storm, using a proper PubSub, and partitioning in Bullet Core, the performance is actually a lot better. However, the point of this performance section is to simply conclude that (Spoilers Ahead) scaling out is pretty linear and queries mostly fit into the overhead of reading the data when the simultaneous queries desired is in the hundreds.

Tools used

Cluster

Data

Configuration

Here is the default configuration we used to launch instances of Bullet.

bullet.topology.metrics.enable: true
bullet.topology.metrics.built.in.enable: true
bullet.topology.metrics.built.in.emit.interval.mapping:
   bullet_active_queries: 5
   default: 60
bullet.topology.metrics.classes:
  - "package.containing.our.custom.class.pushing.metrics"
bullet.topology.tick.interval.secs: 1
bullet.query.default.duration: 30000
bullet.query.max.duration: 540000
bullet.query.aggregation.max.size: 512
bullet.query.aggregation.raw.max.size: 500
bullet.query.aggregation.distribution.max.points: 200

Any setting not listed here defaults to the defaults in bullet_defaults.yaml. In particular, metadata collection and timestamp injection is enabled. RAW type queries also micro-batch by size 1 (in other words, do not micro-batch).

The parallelisms, CPU and memory settings for the components are listed below.

Testing on Kafka 0.9.0.1

For Tests 1 through 4, we read from a Kafka 0.9 cluster with the following configuration for the various Bullet components (unless specified). We use the single Spout model to read from the Kafka topic, partitioned into 64 partitions.

Resource utilization

Component Parallelism CPU (cores) On Heap Memory (MiB) Off Heap Memory (MiB) Total Memory (MiB)
DataSource Spout 64 64 768.0 192.0 61440
Filter Bolt 128 128 384.0 192.0 73728
Join Bolt 2 1 384.0 192.0 1152
DRPC Spout 2 0.4 128.0 192.0 640
PrepareRequest Bolt 1 0.2 128.0 192.0 320
ReturnResults Bolt 1 0.2 128.0 192.0 320
IMetricsConsumer 1 0.1 128.0 0 128
Ackers 256 25.6 128.0 0 32768
Total 455 219.5 170496

With our ~47 virtual core machines, we would need 5 of these machines to run this instance of Bullet reading this data source and supporting a certain number of queries. What this certain number is, we will determine below.

The topology was also launched (command-line args to Storm) with the following Storm settings:

storm jar
    ...
    --bullet-spout-parallelism 64
    --bullet-spout-cpu-load 100.0 \
    --bullet-spout-on-heap-memory-load 768.0 \
    --bullet-spout-off-heap-memory-load 192.0 \
    -c topology.acker.executors=256 \
    -c topology.max.spout.pending=20000 \
    -c topology.backpressure.enable=false \
    -c topology.worker.max.heap.size.mb=4096.0 \
    -c topology.worker.gc.childopts="-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:NewSize=128m -XX:CMSInitiatingOccupancyFraction=70 -XX:-CMSConcurrentMTEnabled -XX:NewRatio=1" \
    ...
  1. The spout parallelism is 64 because it is going to read from a Kafka topic with 64 partitions (any more is meaningless since it cannot be split further). It reads and converts the data into Bullet Records.
  2. We've fanned out from the spouts to the Filter Bolts by a ratio of 2. We may or may not need this.
  3. We use topology.max.spout.pending=20000 to limit the number of in-flight tuples there can be from a DataSource Spout instance and throttle it if too many queries are slowing down processing downstream. This is set pretty high to account for catch-up and skew in our Kafka partitions
  4. We have set the max heap size for a worker to 4 GiB since we do not want too large of a worker. If a component dies or a worker is killed by RAS, it will not affect too many other components. It also makes heap dumps etc manageable.
  5. We set topology.worker.gc.childopts to use ParNewGC and CMS. These are our cluster defaults but we are listing them here since this may not be true for all Storm clusters. We have also added the -XX:NewRatio=1 to the defaults since most of our objects are short-lived and having a larger Young Generation reduces our Young Generation GC (ParNew) frequency.
  6. We are using 256 acker tasks. There is acking from the DataSource Spout to the Filter Bolt and from the DRPCSpout and the PrepareRequestBolt, so about ~130 components will be acking. We could get away with using much less ackers as they are very light-weight.

Test 1: Measuring the minimum latency of Bullet

We are running this query in this test. This RAW query without any filters will serve to measure the intrinsic delay added by Bullet. The data record pulled out has a timestamp for when the record was emitted into Kafka, Bullet will inject the timestamp into the record when the Filter Bolt sends it on and the metadata collection logs timestamps for when the query was received and terminated. Using these, we can measure the end-to-end latency for getting one record through Bullet.

Result

The following table shows the timestamps averaged by running 100 of these queries. The delays below are shown relative to the Query Received timestamp (when the query was received by Bullet at the Join Bolt).

Timestamp Delay (ms)
Kafka Received -710.75
Bullet Filtered -2.16
Query Received 0
Query Finished 1.66

The Bullet Filtered timestamp above is negative because the Filter Bolt received the query and emitted an arbitrary record 2.16 ms before the Join Bolt received the query. The data was submitted into Kafka about 710.75 ms before the query was received by Bullet and that difference is the processing time of Kafka and the time for our spouts to read the data into Bullet.

Conclusion

Bullet adds a delay of a few ms - 1.66 ms in the test above - to just pull out a record. This result shows that this is the fastest Bullet can be. It cannot return data any faster than this for meaningful queries.

Test 2: Measuring the time to find a record

The last test attempted to measure how long Bullet takes to pick out a record. Here we will measure how long it takes to find a record that we generate. This is the average of running 100 queries across a time interval of 30 minutes trying to filter for a record with a single unique value in a field similar to this query.

We added a timestamp into the record when the record was initially read by the DataSource Spout. Using this and the Bullet Filtered timestamp and Query Finished timestamps, we can easily track the record through Bullet.

Since we are looking at values in the data, the average data volume across this test was: Data: 76,000 R/s and 101 MiB/s

Result

Timestamp Delay (ms)
Kafka Received 445.7
Bullet Received 996.5
Bullet Filtered 1003.3
Query Received 0
Query Finished 1006.8

The record was emitted into Kafka 445.81 ms after the query was received. The delay is the time it takes for the generated record to flow through our network and into Kafka.

Bullet received the record 996.5 ms after the query was received. The delay from when Kafka received the record to Bullet received is the delay for Kafka to make the record available for reading.

Conclusion

We see that Bullet took on average 1006.8 ms - 996.5 ms or 10.3 ms from the time it saw the record first in DataSource Spout to finishing up the query and returning it in the Join Bolt.

Test 3: Measuring the maximum number of parallel RAW queries

This test runs a query similar to the simple filtering query. The query looks for 10 records that match the filter or runs for 30 seconds, whichever comes first. The average, uncompressed record size was about 1.8 KiB.

What is meant by maximum?

We want to see how many of these queries we can have running simultaneously till the Filter Bolt is unable to process records from the spouts in time. If a Filter Bolt is unable to keep up with the rate of data produced by the spouts, our queries will not find all 10 records. Workers may start dying (killed by RAS for exceeding capacity) as well. We will be trying to find the number of queries in parallel that we can run without these happening.

The average data volume across this test was: Data: 85,000 R/s and 126 MiB/s

Query

{
 "filters" : [
              {"field" : "id", "operation" : "==", "values": ["c39ba8cfe8"]}
             ],
 "aggregation" : {"type" : "LIMIT", "size" : 10},
 "duration" : 30000
}

We will run a certain number of these queries then generate records matching this query. We will validate that we have all 10 records for all queries at the end.

We ran a number of queries in parallel (you may have to use ulimit to change maximum user processes if you specify a large number), then generated data for the queries (the same data) and waited till the results came back. We then used jq to validate that all generated data was present. In a later test, we will actually measure the latency increase caused by increasing the queries.

  1. It generates a provided number of the query above and runs them in parallel against a randomly chosen DRPC server
  2. It generates data for the query
  3. It waits out the rest of the time and uses jq to validate that all the generated data was found

Result

We were able to run 200 queries successfully but 300 and higher started causing our Filter Bolts to slow down. This slow down caused our spouts to be throttled and fall behind reading data. This caused the matching data to not show up in time during the queries. Some of our attempts would not return all the expected 10 records.

Using our metrics that were captured using our in-house metrics aggregation system (that our IMetricsConsumer publishes to), let's take a look at the CPU, Heap utilizations.

Before you look at the figures:

  1. All the figures below are for the same time interval. The X-axis represents time in 1 minute intervals
  2. Figure 1 shows the number of queries running for a time interval
  3. The other figures show a metric across all the workers (JVMs) in the Storm topology, each running a mix of a components (spouts reading from Kafka, Filter Bolts etc)
  4. The majority of the components (excluding ackers) are spouts reading from Kafka or Filter Bolts, so the figures can be taken to be primarily describing those workers

Figure 1. Queries running

Queries

Figure 2. CPU user-time usage

CPU Utilization

Figure 3. On Heap usage

Heap Utilization

Figure 4. Garbage Collection times

GC Time

Figure 1 shows that we first ran 100 queries, then 200, then 400 and finally 300. The numbers go over their target because we only added a 2 s buffer in our script. Network and tick delays caused some queries to not be entirely purged before the next set of N simultaneous queries came in.

Figure 2 shows the milliseconds of CPU time used per minute. For example, a value of 300K ms ms for a line (worker) means that the worker used 300K ms/min or 300s/60s or 5 CPU cores (virtual) in that minute.

Figure 3 shows raw numbers for Heap utilizations in bytes.

Figure 4 shows the time spent garbage collecting in ms.

Garbage collection

As we increase the number of queries sent into Bullet, more objects are created in the Filter and Join Bolts. These quickly fill up our heap and cause GCs. The zig-zags represents heaps being cleared after GC and filling back up quickly. Also, note that the CPU usage is directly related to the GC times. In other words, performance is pretty much directly correlated with the amount of GC we do.

The following table summarizes these figures:

Simultaneous Queries Average CPU (ms) Average Result size
0 90K N/A
100 130K 10
200 170K 10
300 230K 8.9
400 270K 7.3

Conclusion

We are able to run somewhere between 200 and 300 RAW queries simultaneously before losing data.

Test 4: Improving the maximum number of simultaneous RAW queries

The last test showed us that the standard configuration lets us run somewhere from 200 and 300 RAW queries. Let's improve that. The GC times and the heap usage tell us that a larger heap may help. Also, since each of our machines has 256 GB of RAM and we have a lot of unused heap being wasted per machine (since we use up all the CPU cores), we can be use a lot more heap and not have to GC so much. Let's also try to make the worker even leaner by decreasing the max worker size so that slow components don't block others.

Changes:

-bullet.topology.filter.bolt.memory.on.heap.load: 384.0
+bullet.topology.filter.bolt.memory.on.heap.load: 1024.0

- --bullet-spout-on-heap-memory-load 768.0 \
+ --bullet-spout-on-heap-memory-load 1280.0 \

- -c topology.worker.max.heap.size.mb=4096.0 \
+ -c topology.worker.max.heap.size.mb=3072.0 \

Our resource utilization is now:

Component Parallelism CPU (cores) On Heap Memory (MiB) Off Heap Memory (MiB) Total Memory (MiB)
DataSource Spout 64 64 1280.0 192.0 94208
Filter Bolt 128 128 1024.0 192.0 155648
Join Bolt 2 1 384.0 192.0 1152
DRPC Spout 2 0.4 128.0 192.0 640
PrepareRequest Bolt 1 0.2 128.0 192.0 320
ReturnResults Bolt 1 0.2 128.0 192.0 320
IMetricsConsumer 1 0.1 128.0 0 128
Ackers 256 25.6 128.0 0 32768
Total 455 219.5 285184

Our data volume across this test was: Data: 84,000 R/s and 124 MiB/s

Result

With this configuration, we were able to run 700 queries simultaneously and failed at some where between 700 and 800. See below for why.

We notice that the GC times have improved a lot (down to ~12K ms from ~35K ms in Figure 4). While our overall CPU usage seems to have gone down since we GC a lot less, remember that our changes to the maximum worker size makes our workers run less components and as a result, use less CPU. This is why there are more lines overall (more workers).

Figure 5. Queries running

Queries

Figure 6. CPU user-time usage

CPU Utilization

Figure 7. On Heap usage

Heap Utilization

Figure 8. Garbage Collection times

GC Time

Simultaneous Queries Average CPU (ms) Average Result size
0 50K N/A
300 80K 10
500 95K 10
600 100K 10
700 100K 10
735 105K 10
800 105K 9.19

We seem to cap out at 735 queries. This is actually due how the blocking implementation of Storm DRPC works. Storm DRPC currently dedicates a thread to each DRPC request and does not allow more requests till they are finished. For Bullet, when we ran 800 queries for the test, only the first 735 would even be sent to Bullet. The rest 65 would be sent after some of the first return but all of those 65 would return 0 records because the data that they are looking for had long since been processed. We had 3 DRPC servers in the cluster and you could scale by adding more of these.

Conclusion

With this change in heap usage, we could get to 735 of these queries simultaneously without any issues. We could do more but were limited by the number of DRPC servers in our cluster.

735 is a hard limit then?

This is what our Storm cluster's configuration and our usage of the Storm DRPC limits us to. There is an async implementation for DRPC that we could eventually switch to. If we used another PubSub implementation like Kafka, we would be able to bypass this limit.

Testing on Kafka 0.10.0.1

For this and subsequent tests, we upgraded our Kafka cluster to 0.10. We used the new Kafka consumer APIs to read batches of messages instead of a message at a time. We changed our DataSource Spout to read batches of messages (raw bytes) instead and added a DataSource Bolt that converts each batch message into Bullet records. Switching to this model let us be a lot more efficient in our data reading.

To read more data, we will be trying to read a topic that is a superset of our data set so far and produces up to 13 times the number of records (maximum of 1.3 million records/sec) and 20 times the size of the data we were reading till now. This Kafka topic has 256 partitions.

Test 5: Reading more Data

Our average data volume across this test was: Data: 756,000 R/s and 3080 MiB/s

Component Parallelism CPU (cores) On Heap Memory (MiB) Off Heap Memory (MiB) Total Memory (MiB)
DataSource Spout 128 128 1024.0 192.0 155648
DataSource Bolt 256 512 2580.0 192.0 709632
Filter Bolt 512 512 1024.0 192.0 622592
Join Bolt 2 1 512.0 192.0 1408
DRPC Spout 2 0.4 128.0 192.0 640
PrepareRequest Bolt 1 0.2 128.0 192.0 320
ReturnResults Bolt 1 0.2 128.0 192.0 320
IMetricsConsumer 4 0.4 128.0 0 512
Ackers 256 25.6 128.0 0 32768
Total 1162 1179.8 1523840

In terms of our machines, the CPU is clearly the limiting factor. We end up using about 25 machines to run this topology.

We also tweaked our GC and Storm settings. We ran the topology with the following command:

storm jar
          ...
          --bullet-conf bullet_settings.yaml \
          -c topology.max.spout.pending=30 \
          -c topology.backpressure.enable=false \
          -c topology.acker.executors=256 \
          -c topology.component.resources.onheap.memory.mb=128.0 \
          -c topology.worker.max.heap.size.mb=3072.0 \
          -c topology.worker.gc.childopts="-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:NewSize=128m -XX:NewRatio=2 -XX:SurvivorRatio=6 -XX:+UseCMSInitiatingOccupancyOnly -XX:-CMSConcurrentMTEnabled -XX:CMSInitiatingOccupancyFraction=50 -XX:ParallelGCThreads=8 -XX:ConcGCThreads=4" \
          ...

We capped the GC threads to 8 and 4, which helps performance on our 48 core machines when multiple JVMs run on a machine. We also bumped up the Young Generation size (NewRatio=2) and triggered the CMS collection to run at 50% of Old Generation instead of the default of 70%. Our objects are short-lived in our streaming scenario, this makes sense. We arrived at this after a few iterations, which we'll skip here for brevity.

Max Spout Pending is now 30 ?!

We use topology.max.spout.pending as a way to throttle how fast we read from Kafka. There is no acking past the Filter Bolt. The maximum number of batch messages we read is 500 from Kafka. This makes our true max spout pending: 500 * 30 = 15,000. The tuple that is emitted from the spout is a large tuple that contains up to 500 records and we limit up to 30 of those to go unacked from any single spout before we throttle it. Since we have 128 spouts, we can have 128 * 15,000 messages unacked in the topology at any time at the most.

Result

We were able to run over 600 queries with this configuration and failed in the high 600s due to hitting the DRPC limit again. With our improved reading model and GC configs, our base resource footprint has improved from 50K CPU ms/min to around 25K CPU ms/min.

Figure 9. Queries running

Queries

Figure 10. CPU user-time usage

CPU Utilization

Figure 11. On Heap usage

Heap Utilization

Figure 12. Garbage Collection times

GC Time

Simultaneous Queries Average CPU (ms) Average Result size
0 25K N/A
100 35K 10
300 60K 10
500 85K 10
600 90K 10
680 95K 10
700 95K 9.79

Note that the drops when we were running simultaneous queries in Figure 9 are due to some hiccups in our collection mechanism (the collection granularity was not 5s as we configured but higher) and not actually drops in the simultaneous queries.

Conclusion

We are trying to read a data source that could have13 times more records and 20 times more data volume. So we have roughly increased the parallelism of the components reading the data by 10x (128 + 512 = 768 cores to read and convert the data whereas previously we were using 64 cores). Once this is fixed and we can read the data comfortably using our DataSource Spouts and Bolts, we can scale the Filter Bolts and other components to accommodate for queries. We set our Filter Bolt parallelism (dominates the rest of the components) to 512. We need about 25 machines (5 times more than the previous of 5).

With this configuration, we were able to run 680 queries simultaneously before we hit the DRPC limit. Since DRPC is a shared resource for the cluster, this limit is slightly lower than the previously observed number possibly due to our test environment being multi-tenant and other topologies using the shared resource.

Measuring latency in Bullet

So far, we have been using data being delayed long enough as a proxy for queries failing. Bullet-Storm 0.4.3 adds an average latency metric computed in the Filter Bolts. For the next tests, we add a timestamp in the Data Source spouts when the record is read and this latency metric tells us exactly how long it takes for the record to be matched against a query and acked. By setting a limit for this latency, we can much more accurately measure acceptable performance.

Test 6: Scaling for More Data

For this test, we'll establish how much resources we need to read various data volumes. We want to be able to:

For reading the data, we have to first scale the DataSource spouts and bolts and then set the parallelism of the Filter bolts to support the minimum 400 queries we want at the data volume. We leave the rest of the components at their default values as seen in in Test 5.

To get various data volumes, we read a large Kafka topic with (256 partitions) with over 1 million R/s and sample various percentages to get less data. The sampling is done in our DataSource Spouts.

Result

The following table summarizes the results:

Data (MiB/s, R/s) Component Parallelism CPU cores On Heap (MiB) Total CPU cores Total Memory (MiB)
307, 69700 98.3 123648
DataSource Spout 16 0.5 1024
DataSource Bolt 32 2 2048
Filter Bolt 24 1 1024
920, 216825 242.7 281856
DataSource Spout 32 1 1024
DataSource Bolt 72 2 2048
Filter Bolt 64 1 1024
1535, 374370 531.5 616192
DataSource Spout 64 1 1024
DataSource Bolt 160 2 2048
Filter Bolt 144 1 1024
2149, 524266 812.3 939264
DataSource Spout 72 1 1024
DataSource Bolt 256 2 2048
Filter Bolt 224 1 1024
3070, 724390 997.1 1321984
DataSource Spout 96 1 1024
DataSource Bolt 320 2 2580
Filter Bolt 256 1 1024
4024, 1004500 1189.4 1582208
DataSource Spout 96 1 1024
DataSource Bolt 384 2 2580
Filter Bolt 320 1 1024

The following figures graphs how the data volume relates to the total CPU and Memory needed.

Figure 13. Data Volume vs CPU

Queries

Figure 14. Data Volume vs Memory

Queries

As these figures show, Bullet scales pretty linearly for more data. For each core of CPU core, we need about 1.2 GiB of Memory. That is the, CPU to Memory ratio is 1 core : 1.2 GiB. The slopes of figures show that the CPU to data ratio is 1 core : 850 R/s or 1 core : 3.4 MiB/s.

Conclusion

This test demonstrates that Bullet scales pretty linearly for reading more data. We were able to support at least 400queries with plenty of headroom for each configuration. Each CPU core required about 1.2 GiB of Memory and gave us roughly 800 R/s or 3.4 MiB/s processing capability. Of course, this is particular to our data. As mentioned in the data section, most of our data was concentrated in random maps. This means that in memory, the data is generally not contiguous. This creates memory fragmentation and more GC pressure. Depending on your data schema, your performance may be a lot better.

Test 7: Scaling for More Queries

For this test, we'll establish how much resources we need to support more queries for a fixed data volume: Data: 68,400 R/s and 105 MiB/s.

As our 3 server DRPC cluster currently does not let us do more than 680 RAW queries, in this test, we will:

Results

The following table summarizes the results:

Filter Bolt Parallelism Queries Average Latency (ms) Status Topology CPU (cores) Topology Memory (MiB)
4 78.3 112256
1 7 OK
10 8 OK
20 8 OK
30 10 OK
40 12 OK
50 167 OK
60 1002 FAIL
8 82.3 117120
40 9 OK
60 9 OK
80 9 OK
100 10 OK
120 14 OK
140 18 OK
160 298 FAIL
170 2439 FAIL
12 86.3 121984
160 13 OK
200 14 OK
240 78 OK
280 274 FAIL
320 680 FAIL
360 1700 FAIL
400 2685 FAIL
16 90.3 126848
300 30 OK
350 44 OK
400 481 FAIL
450 935 FAIL
500 1968 FAIL
550 3267 FAIL
20 94.3 131712
350 15 OK
400 18 OK
450 28 OK
500 40 OK
550 670 FAIL
600 1183 FAIL
650 1924 FAIL
24 98.3 136576
450 17 OK
500 22 OK
550 30 OK
600 377 FAIL
650 490 FAIL
28 102.3 141440
550 39 OK
600 53 OK
650 468 FAIL
32 106.3 146304
600 26 OK
650 32 OK

The following figure summarizes the minimum number of CPU cores (which are also the number of Filter Bolts) needed to support the the maximum number of RAW queries with latency < 200 ms.

Figure 15. CPU vs Max Concurrent Queries

Queries

This shows that the queries supported also scale pretty linearly.

You may have noticed how when latency starts to increase, it increases pretty rapidly. This suggests that there is a knee or exponential curve for latency. The following figure shows this in the graph of the latency for queries with 20 Filter Bolts.

Figure 16. Max Concurrent Queries vs Latency

Queries

Conclusion

Since Filter Bolts tend to be the most CPU intensive of the query processing components, this test measured how scaling Filter Bolts affected the number of queries that can be supported. For the fixed data volume, this relationship is linear.