This directive specifies the percentage of hash-table buckets Squid scans during each call to the digest rebuild procedure. Squid services normal cache traffic in between these calls. Since this scanning is CPU-intensive, user requests may be delayed for a small, but noticeable amount of time. If you suspect a performance problem during the rebuild phase, decrease the digest_rebuild_chunk_percentage value.
digest_generation, digest_rebuild_period, store_objects_per_bucket