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perf(compile): rebalance disk from build variants to ccache 

Measured on staging: 46 per-variant build trees held 25 GB - each one a
full copy of the same ESP-IDF component objects - while ccache, the
cache that serves EVERY target and variant, was capped at 8 GB and
permanently full: 99.97% of its limit, 153 evictions, 47% lifetime hit
rate. Objects were being thrown out before they could be reused, so
builds recompiled work they had already done.

Variant cap 12 -> 6 and ccache 8G -> 20G. The asymmetry is deliberate:
an evicted variant dir rebuilds quickly FROM ccache, whereas a ccache
miss recompiles from source. Pruning the cold variants freed 8 GB on
the staging box (88% -> 84% disk) before the larger cache can grow into
it.
This commit is contained in:
David Montero Crespo 2026-08-20 06:28:46 +02:00
parent 82f25a03c4
commit be0f470239
2 changed files with 8 additions and 2 deletions
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2
Dockerfile.standalone
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@ -308,7 +308,7 @@ ENV CCACHE_NOHASHDIR=1
# runtime by the volume mount. ccache reads CCACHE_MAXSIZE / CCACHE_COMPRESS # runtime by the volume mount. ccache reads CCACHE_MAXSIZE / CCACHE_COMPRESS
# / CCACHE_COMPRESSLEVEL on every invocation and they override any conf-file # / CCACHE_COMPRESSLEVEL on every invocation and they override any conf-file
# value, so the cap actually applies at runtime. # value, so the cap actually applies at runtime.
ENV CCACHE_MAXSIZE=8G ENV CCACHE_MAXSIZE=20G
ENV CCACHE_COMPRESS=1 ENV CCACHE_COMPRESS=1
ENV CCACHE_COMPRESSLEVEL=6 ENV CCACHE_COMPRESSLEVEL=6
RUN mkdir -p /var/cache/ccache /var/lib/velxio-build /root/Arduino RUN mkdir -p /var/cache/ccache /var/lib/velxio-build /root/Arduino

8
backend/app/services/espidf_compiler.py
View File

@ -219,7 +219,13 @@ def _run_with_streaming(
# coldest. Each variant is a full ESP-IDF build tree (~240 MB). Distinct # coldest. Each variant is a full ESP-IDF build tree (~240 MB). Distinct
# variants = distinct (board options x resolved library set). The global ccache # variants = distinct (board options x resolved library set). The global ccache
# means an evicted-then-rebuilt variant warms up in seconds. # means an evicted-then-rebuilt variant warms up in seconds.
_MAX_BUILD_VARIANTS = 12 # Was 12. Each variant is a FULL ~1 GB build tree holding its own copies of
# the same ESP-IDF component objects, so 46 of them had grown to 25 GB while
# ccache - the cache that actually serves EVERY target and variant - sat
# capped at 8 GB, permanently full (99.97%, 153 evictions, 47% hit rate).
# Fewer trees, a bigger shared cache: a variant that gets evicted rebuilds
# quickly FROM ccache, but a ccache miss recompiles from source.
_MAX_BUILD_VARIANTS = 6
def _evict_cold_variants(target_dir: Path, keep: int) -> None: def _evict_cold_variants(target_dir: Path, keep: int) -> None: