# [Run a new workload using BOLT and merge the results](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-3/)

## In this learning path

- [Introduction](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/)
- [Overview](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-1/)
- [Instrument MySQL with BOLT](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-2/)
- [Run a new workload using BOLT and merge the results](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-3/)
- [Instrument shared libraries with BOLT](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-4/)
- [Review the performance results](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/how-to-5/)
- [Next Steps](https://learn.arm.com/learning-paths/servers-and-cloud-computing/bolt-merge/_next-steps/)

## Overview
In this step, you’ll generate a profile for a write-heavy workload and merge it with the read-heavy profile you created earlier. The merged profile captures a broader set of execution behaviors for optimizing the final binary.

## Run a write-only workload for the application binary
You can reuse the previously built MySQL binary or generate a new instrumented variant if needed.

Use the BOLT-instrumented MySQL binary to run a write-only workload and generate `profile-writeonly.fdata`. You can reuse the binary from the previous step or create a new one with the command below.

```
llvm-bolt $HOME/mysql-server/build/bin/mysqld \
  -instrument \
  -o $HOME/mysql-server/build/bin/mysqldwriteonly.instrumented \
  --instrumentation-file=$HOME/mysql-server/build/profile-writeonly.fdata \
  --instrumentation-sleep-time=5 \
  --instrumentation-no-counters-clear \
  --instrumentation-wait-forks 2>&1 | tee $HOME/mysql-server/bolt-instrumentation-writeonly.log
```

## Run the write-only workload
Run Sysbench using the write-only Lua script to generate a workload profile:

```
# On an 8-core system, use available cores (e.g., 7 for Sysbench)
taskset -c 7 ./src/sysbench \
  --db-driver=mysql \
  --mysql-host=127.0.0.1 \
  --mysql-db=bench \
  --mysql-user=bench \
  --mysql-password=bench \
  --mysql-port=3306 \
  --tables=8 \
  --table-size=10000 \
  --forced-shutdown \
  --report-interval=60 \
  --rand-type=uniform \
  --time=5 \
  --threads=1 \
  --simple-ranges=1 \
  --distinct-ranges=1 \
  --sum-ranges=1 \
  --order-ranges=1 \
  --point-selects=10 \
  src/lua/oltp_write_only.lua run
```

Confirm that `--instrumentation-file` is set to `profile-writeonly.fdata`.

## Reset the dataset after profiling
After running each benchmark, cleanly shut down the MySQL server and reset the in-memory dataset to ensure the next run starts in a consistent state:

```
./bin/mysqladmin -u root shutdown ; rm -rf /dev/shm/dataset ; cp -R data/ /dev/shm/dataset
```

## Verify that both profiles exist
Verify that the following `.fdata` files have been generated:

```
ls -lh $HOME/mysql-server/build/profile-readonly.fdata
ls -lh $HOME/mysql-server/build/profile-writeonly.fdata
```

## Merge the read and write profiles
Both `.fdata` files should now exist and contain valid data:

- `profile-readonly.fdata`
- `profile-writeonly.fdata`

## Merge the feature profiles
Use `merge-fdata` to combine the feature-specific profiles into one comprehensive `.fdata` file:

```
merge-fdata $HOME/mysql-server/build/profile-readonly.fdata $HOME/mysql-server/build/profile-writeonly.fdata \
  -o $HOME/mysql-server/build/profile-merged.fdata
```

Output:
```
Using legacy profile format.
Profile from 2 files merged.
```

This creates a single merged profile (`profile-merged.fdata`) covering both read-only and write-only workload behaviors.

## Verify the merged profile
Confirm the merged profile file exists and is non-empty:

```
ls -lh $HOME/mysql-server/build/profile-merged.fdata
```

## Optimize the binary with the merged profile
Use LLVM-BOLT to generate the final optimized binary using the merged `.fdata` file:

```
llvm-bolt $HOME/mysql-server/build/bin/mysqld \
  -o $HOME/mysql-server/build/bin/mysqldreadwrite_merged.bolt_instrumentation \
  -data=$HOME/mysql-server/build/profile-merged.fdata \
  -reorder-blocks=ext-tsp \
  -reorder-functions=hfsort \
  -split-functions \
  -split-all-cold \
  -split-eh \
  -dyno-stats \
  --print-profile-stats 2>&1 | tee $HOME/mysql-server/build/bolt-readwritemerged-opt.log
```

**Key flags explained:**

- `-reorder-blocks=ext-tsp`: Reorders code blocks to improve cache locality
- `-split-functions`: Separates hot and cold regions for better performance
- `-dyno-stats`: Prints dynamic profile-based statistics during optimization

This command optimizes the binary layout based on the merged workload profile, creating a single binary (`mysqldreadwrite_merged.bolt_instrumentation`) that is optimized across both features.