“索引下降”表示“缓存查询因约束而失败”

Question

我有这张桌子。

                                          Table "public.tree"
        Column        |            Type             |                     Modifiers                     
----------------------+-----------------------------+---------------------------------------------------
 id                   | integer                     | not null default nextval('tree_id_seq'::regclass)
 name                 | character varying(128)      | 
 state                | character varying(128)      | 
Indexes:
    "tree_pkey" PRIMARY KEY, btree (id)
    "tree_name_key" UNIQUE, btree (name)
    "unicity_name_state" UNIQUE CONSTRAINT, btree (name, state)

我的目标是删除索引“ tree_name_key”。

但是当我尝试删除它时，我遇到了一个错误

# drop index tree_name_key;
ERROR:  cache lookup failed for constraint 16541

可能是什么问题？