Spider has many plugin variables regarding table statistics but they looks redundant. Reorganize them as the following:
|New variable||Corresponding old variables||Comment|
|spider_store_last_crd, spider_store_last_sts, spider_load_crd_at_startup, spider_load_sts_at_startup||Always persist stats if sync is ON.|
|spider_crd_mode, spider_sts_mode||Use SHOW TABLE/INDEX always.|
|spider_sync_stats_enabled||spider_crd_bg_mode, spider_crd_sync, spider_bg_sts_mode, spider_sts_sync||0: no sync, 1: sync background|
|spider_table_crd_thread_count, spider_table_sts_thread_count||A single thread for both crd and sts seems to be enough.|
|spider_crd_type, spider_crd_weight||Make it adaptive someday.|
- Ultimately, I think all parameters should be removed (the best settings should be applied automatically).
- Does it make sense to disable stats synchronization, in the first place?