BE Multi-Directory Shared Cache

When working with AI Agents for Doris BE development, a common pattern is to use git worktree or similar methods to maintain multiple development branches in different directories simultaneously. Due to ccache's sensitivity to full path names, even when the majority of cpp files are identical across different directories, ccache cannot hit the cache, causing worktree directories to recompile from scratch, significantly slowing down development. To address this issue, we have implemented custom optimizations that can be configured as follows:

Directory Requirements

Doris has already set CCACHE_BASEDIR and -ffile-prefix-map in the environment configuration file, mapping most compilation options to the same path for cache hit. The premise is that all Doris development directories must share the same parent directory. All Doris development directories must satisfy relationship like this:

xxx/doris_main
xxx/doris1
xxx/doris2

Environment Configuration

1. In addition to the above settings, hardcoded paths still need to be manually adjusted. The UBSAN IGNORELIST of the main repository needs to be hardcoded in the custom_env.sh of the worktree directory:

export UBSAN_IGNORELIST=${DORIS_MAIN_REPO}/conf/ubsan_ignorelist.txt

Where DORIS_MAIN_REPO is the path to the main repository. We recommend configuring this value directly in the main repository's custom_env.sh, and having the AI workflow automatically pass it to all worktree directories through hooks/setup_worktree.sh and AGENTS.md.

2. To ensure sufficient cache space, manually increase the ccache cache capacity:

ccache --set-config=max_size=50G

Debug Method

You can use ccache -s to view cache statistics and confirm whether the cache is working. Pay attention to the cache hit rate field; if the value is too low, it indicates the cache is not being hit correctly. Before each observation, you can use ccache -z to clear the statistics to ensure accurate results. When cache hits are problematic, you can enable ccache debug logs to confirm:

export CCACHE_LOGFILE=/path/to/xxx
export CCACHE_DEBUG=1

You can view detailed cache hit information in CCACHE_LOGFILE to help identify issues. After enabling CCACHE_DEBUG=1, each compilation unit will generate its own *.ccache-input-text file, recording the input information of that compilation unit, including source file paths and compilation options. Theoretically, the same file in two different directories must have completely identical ccache-input-text content to hit the ccache cache. For files that fail to hit the cache, you can examine the differences between the two ccache-input-text files to identify the reasons for the cache miss.