次の sql を高速化したい (コストは 19685.75)。複数の複雑なネストされた AND 条件が WHERE ステートメントで OR と組み合わされているこの SQL にインデックスを付けることはできますか?
SELECT DISTINCT
ON ("crawler_url"."url") U0."id"
FROM "characteristics_text" U0 LEFT OUTER
JOIN "characteristics_text_urls"
ON (U0."id" = "characteristics_text_urls"."text_id") LEFT OUTER
JOIN "crawler_url"
ON ("characteristics_text_urls"."url_id" = "crawler_url"."id")
WHERE (
(
U0."publication_date" BETWEEN '2018-01-01' AND '2018-12-31'
AND EXTRACT('month' FROM U0."publication_date") = 10
)
OR
(
U0."publication_date" IS NULL
AND U0."lastmod" BETWEEN '2018-01-01' AND '2018-12-31'
AND EXTRACT('month' FROM U0."lastmod") = 10
)
OR
(
U0."publication_date" IS NULL
AND U0."lastmod" IS NULL
AND U0."created_at" BETWEEN '2018-01-01 00:00:00+08:00' AND '2018-12-31 23:59:59.999999+08:00'
AND EXTRACT('month' FROM U0."created_at" AT TIME ZONE 'Asia/Hong_Kong') = 10
)
OR
(
U0."publication_date" >= '2018-08-01'
AND U0."publication_date" < '2018-10-31'
)
OR
(
U0."publication_date" IS NULL
AND U0."lastmod" >='2018-08-01'
AND U0."lastmod" < '2018-10-31'
)
OR
(
U0."publication_date" IS NULL
AND U0."lastmod" IS NULL
AND U0."created_at" >= '2018-07-31 16:00:00+00:00'
AND U0."created_at" < '2018-10-30 16:00:00+00:00'
)
)
ORDER BY "crawler_url"."url" ASC, U0."created_at" DESC
テーブル テキストには、次のフィールドとインデックスが含まれています (他のフィールドは表示されていません)。
Table "public.characteristics_text"
Column | Type | Modifiers
------------------------+--------------------------+-------------------------------------------------------------------
id | integer | not null default nextval('characteristics_text_id_seq'::regclass)
text | text |
created_at | timestamp with time zone | not null
lastmod | date |
publication_date | date |
Indexes:
"characteristics_text_pkey" PRIMARY KEY, btree (id)
"characteristics_text_fde81f11" btree (created_at)
"characteristics_text_lastmod_3bff34c2_uniq" btree (lastmod)
"characteristics_text_publication_date_772c1bda_uniq" btree (publication_date)
"characteristics_text_publication_date_c6311385_idx" btree (publication_date, lastmod, created_at)
created_at、lastmod、publication_date の 3 つの単一インデックスを追加しました。これらのフィールドの 1 つの複数列インデックス。
しかし、postgres EXPAIN クエリでは、この where 句はまだSeq Scanを使用していますが、 Index Scanは使用していません。
-> Seq Scan on characteristics_text u0 (cost=0.00..19685.75 rows=14535 width=12)
Filter: (
(
(publication_date >= '2018-01-01'::date) AND
(publication_date <= '2018-12-31'::date) AND
(
date_part(
'month'::text, (publication_date)::timestamp without time zone
) = 10::double precision)
) OR
((publication_date IS NULL) AND (lastmod >= '2018-01-01'::date) AND (lastmod <= '2018-12-31'::date) AND (date_part('month'::text, (lastmod)::timestamp without time zone) = 10::double precision)) OR ((publication_date IS NULL) AND (lastmod IS NULL) AND (created_at >= '2017-12-31 16:00:00+00'::timestamp with time zone) AND (created_at <= '2018-12-31 15:59:59.999999+00'::timestamp with time zone) AND (date_part('month'::text, timezone('Asia/Hong_Kong'::text, created_at)) = 10::double precision)) OR ((publication_date >= '2018-08-01'::date) AND (publication_date < '2018-10-31'::date)) OR ((publication_date IS NULL) AND (lastmod >= '2018-08-01'::date) AND (lastmod < '2018-10-31'::date)) OR ((publication_date IS NULL) AND (lastmod IS NULL) AND (created_at >= '2018-07-31 16:00:00+00'::timestamp with time zone) AND (created_at < '2018-10-30 16:00:00+00'::timestamp with time zone))
)
私の質問は次のとおり
です。1. この複雑な SELECT 句にインデックス スキャンを使用するように postgres を作成することは可能ですか?
2. AND 句ごとに 1 つの複数列インデックスを作成する必要がありますか? たとえば(publication_date, lastmod)、この原因でインデックスを作成しますか?
(
U0."publication_date" IS NULL
AND U0."lastmod" BETWEEN '2018-01-01' AND '2018-12-31'
AND EXTRACT('month' FROM U0."lastmod") = 10
)
- インデックスは IS NULL の検索で機能しますか? IS NULL のフィールド検索はインデックスにする必要がありますか?
2018 年 11 月 4 日更新
フィールドを 1 つずつテストしてクエリを最小化しようとすると、フィールドpublication_dateとlast_modトリガー インデックス スキャンが個別に行われますが、次のcreated_atことはできません。
created_atタイムスタンプだからですか？しかし、タイムスタンプのインデックスが機能しないのはなぜですか?
explain SELECT DISTINCT
ON ("crawler_url"."url") U0."id"
FROM "characteristics_text" U0 LEFT OUTER
JOIN "characteristics_text_urls"
ON (U0."id" = "characteristics_text_urls"."text_id") LEFT OUTER
JOIN "crawler_url"
ON ("characteristics_text_urls"."url_id" = "crawler_url"."id")
WHERE (
(
U0."created_at" BETWEEN '2018-01-01 00:00:00+08:00' AND '2018-12-31 23:59:59.999999+08:00'
AND EXTRACT('month' FROM U0."created_at" AT TIME ZONE 'Asia/Hong_Kong') = 10
)
)
ORDER BY "crawler_url"."url" ASC, U0."created_at" DESC
Unique (cost=18004.05..18006.01 rows=393 width=86)
-> Sort (cost=18004.05..18005.03 rows=393 width=86)
Sort Key: crawler_url.url, u0.created_at
-> Nested Loop Left Join (cost=0.71..17987.11 rows=393 width=86)
-> Nested Loop Left Join (cost=0.42..17842.25 rows=393 width=16)
-> Seq Scan on characteristics_text u0 (cost=0.00..15467.37 rows=393 width=12)
Filter: ((created_at >= '2017-12-31 16:00:00+00'::timestamp with time zone) AND (created_at <= '2018-12-31 15:59:59.999999+00'::timestamp with time zone) AND (date_part('month'::text, timezone('Asia/Hong_Kong'::text, created_at)) = 10::double precision))
-> Index Scan using characteristics_text_urls_65eb77fe on characteristics_text_urls (cost=0.42..6.03 rows=1 width=8)
Index Cond: (u0.id = text_id)
-> Index Scan using crawler_url_pkey on crawler_url (cost=0.29..0.36 rows=1 width=78)
Index Cond: (characteristics_text_urls.url_id = id)
publication_dateトリガーインデックススキャンのようです：
(
U0."publication_date" IS NULL
AND U0."lastmod" >='2018-08-01'
AND U0."lastmod" < '2018-10-31'
)
Unique (cost=17053.26..17085.63 rows=6473 width=86)
-> Sort (cost=17053.26..17069.44 rows=6473 width=86)
Sort Key: crawler_url.url, u0.created_at
-> Nested Loop Left Join (cost=11130.73..16643.51 rows=6473 width=86)
-> Hash Right Join (cost=11130.44..14257.63 rows=6473 width=16)
Hash Cond: (characteristics_text_urls.text_id = u0.id)
-> Seq Scan on characteristics_text_urls (cost=0.00..1858.01 rows=120601 width=8)
-> Hash (cost=11049.53..11049.53 rows=6473 width=12)
-> Bitmap Heap Scan on characteristics_text u0 (cost=186.95..11049.53 rows=6473 width=12)
Recheck Cond: ((publication_date IS NULL) AND (lastmod >= '2018-08-01'::date) AND (lastmod < '2018-10-31'::date))
-> Bitmap Index Scan on characteristics_text_publication_date_c6311385_idx (cost=0.00..185.33 rows=6473 width=0)
Index Cond: ((publication_date IS NULL) AND (lastmod >= '2018-08-01'::date) AND (lastmod < '2018-10-31'::date))
-> Index Scan using crawler_url_pkey on crawler_url (cost=0.29..0.36 rows=1 width=78)
Index Cond: (characteristics_text_urls.url_id = id)