Postgresql numeric values lost precision

[yuezhuangshi]

Hi,

I'm working with postgresql and insert 18.54322356 to a numeric field with 8 scale, but actually I got 18.54320000.
I also run sql in the database directly and the results is as same as my input.
INSERT INTO http_poller(id, name, birthdate, isrich, money) VALUES(5555, '2', '2018-01-05T02:02:02.000', true, 18.04623585)

output received:(money is the field lost precision)
[2018-08-15T13:49:18,128][DEBUG][logstash.pipeline ] output received {"event"=>{"id"=>1431, "name"=>"leader1431", "@timestamp"=>2018-08-15T05:49:18.019Z, "type"=>"mongo", "tags"=>["leader"], "rich"=>true, "http_poller_metadata"=>{"name"=>"leaderservice", "runtime_seconds"=>0.0032660000000000002, "response_message"=>"OK", "host"=>"jasper.local", "times_retried"=>0, "code"=>200, "response_headers"=>{"connection"=>"keep-alive", "transfer-encoding"=>"chunked", "content-type"=>"application/json;charset=UTF-8", "date"=>"Wed, 15 Aug 2018 05:49:18 GMT"}, "request"=>{"url"=>"http://localhost:8080/leader", "method"=>"get"}}, "@version"=>"1", "birthdate"=>"2018-08-15T13:49:18.018", "money"=>18.65423154}}
statement:
statement => ["insert into http_poller(id, name, birthdate, isrich, money) values(?,?,CAST(? AS timestamp),?,?)","[id]", "[name]", "[birthdate]", "[rich]", "[money]"]
table structure:
`

---

-- Table structure for http_poller

---

DROP TABLE IF EXISTS "public"."http_poller";
CREATE TABLE "public"."http_poller" (
"id" int4 NOT NULL,
"name" varchar(255) COLLATE "pg_catalog"."default" NOT NULL,
"birthdate" timestamp(6) NOT NULL,
"isrich" bool NOT NULL,
"money" numeric(255,8) NOT NULL
)
;
ALTER TABLE "public"."http_poller" OWNER TO "centos";
COMMENT ON COLUMN "public"."http_poller"."birthdate" IS ' ';

---

-- Primary Key structure for table http_poller

---

ALTER TABLE "public"."http_poller" ADD CONSTRAINT "http_poller_pkey" PRIMARY KEY ("id");
`

environment:
logstash-6.3.2
logstash-output-jdbc plugin installed by using logstash-plugin install logstash-output-jdbc
postgresql 9.6.2

I don't know how it happened, can you help me?