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1. When '--execution_log_json_file' is used, we don't need to download code and use execution log parser to convert the logs to
    text anymore. We could directly use our favourite text differ to diff.
   This option is more convenient than '--execution_log_binary_file'.

2. Add information about 'internal' and update example with that.

Closes #14099.

PiperOrigin-RevId: 403899679
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ecngtng authored and copybara-github committed Oct 18, 2021
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49 changes: 16 additions & 33 deletions site/docs/remote-execution-caching-debug.md
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Expand Up @@ -23,12 +23,14 @@ from a remote cache is displayed as `remote cache hit`.

For example:

INFO: 7 processes: 3 remote cache hit, 4 remote.
INFO: 11 processes: 6 remote cache hit, 3 internal, 2 remote.

In this example there were 3 remote cache hits, and 4 actions did not have
cache hits and were executed remotely. Local cache hits are not included in this
summary. If you are getting 0 processes (or a number lower than expected),
run `bazel clean` followed by your build/test command.
In this example there were 6 remote cache hits, and 2 actions did not have
cache hits and were executed remotely. The 3 internal part can be ignored.
It is typically tiny internal actions, such as creating symbolic links. Local
cache hits are not included in this summary. If you are getting 0 processes
(or a number lower than expected), run `bazel clean` followed by your build/test
command.

## Troubleshooting cache hits

Expand All @@ -49,7 +51,7 @@ If you are not getting the cache hit rate you are expecting, do the following:
machine).

4. Check the `INFO` line for cache hit rate. If you see no processes except
`remote cache hit`, then your cache is being correctly populated and
`remote cache hit` and `internal`, then your cache is being correctly populated and
accessed. In that case, skip to the next section.

5. A likely source of discrepancy is something non-hermetic in the build causing
Expand All @@ -59,9 +61,9 @@ If you are not getting the cache hit rate you are expecting, do the following:
a. Re-run the build(s) or test(s) in question to obtain execution logs:

bazel clean
bazel $YOUR_FLAGS build //your:target --execution_log_binary_file=/tmp/exec1.log
bazel $YOUR_FLAGS build //your:target --execution_log_json_file=/tmp/exec1.json
bazel clean
bazel $YOUR_FLAGS build //your:target --execution_log_binary_file=/tmp/exec2.log
bazel $YOUR_FLAGS build //your:target --execution_log_json_file=/tmp/exec2.json

b. [Compare the execution logs](#comparing-the-execution-logs) between the
two runs. Ensure that the actions are identical across the two log files.
Expand Down Expand Up @@ -114,13 +116,13 @@ not happening across machines, do the following:
2. Run the build on the first machine:

bazel clean
bazel ... build ... --execution_log_binary_file=/tmp/exec1.log
bazel ... build ... --execution_log_json_file=/tmp/exec1.json

3. Run the build on the second machine, ensuring the modification from step 1
is included:

bazel clean
bazel ... build ... --execution_log_binary_file=/tmp/exec2.log
bazel ... build ... --execution_log_json_file=/tmp/exec2.json

4. [Compare the execution logs](#comparing-the-execution-logs) for the two
runs. If the logs are not identical, investigate your build configurations
Expand All @@ -138,27 +140,8 @@ logs are identical then so are the action cache keys.
To compare logs for two builds that are not sharing cache hits as expected,
do the folowing:

1. Get the execution logs from each build and store them as `/tmp/exec1.log` and
`/tmp/exec2.log`.
1. Get the execution logs from each build and store them as `/tmp/exec1.json` and
`/tmp/exec2.json`.

2. Download the Bazel source code and navigate to the Bazel folder by using
the command below. You need the source code to parse the
execution logs with the
[execlog parser](https://source.bazel.build/bazel/+/master:src/tools/execlog/).

git clone https://github.com/bazelbuild/bazel.git
cd bazel

3. Use the execution log parser to convert the logs to text. The following
invocation also sorts the actions in the second log to match the action order
in the first log for ease of comparison.

bazel build src/tools/execlog:parser
bazel-bin/src/tools/execlog/parser \
--log_path=/tmp/exec1.log \
--log_path=/tmp/exec2.log \
--output_path=/tmp/exec1.log.txt \
--output_path=/tmp/exec2.log.txt

4. Use your favourite text differ to diff `/tmp/exec1.log.txt` and
`/tmp/exec2.log.txt`.
2. Use your favourite text differ to diff `/tmp/exec1.json` and
`/tmp/exec2.json`.

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