performance - Postgresqlストアド関数の実行が非常に遅い場合がある

Question

PostgreSQL 9.4.4 には、if ステートメントと elsif ステートメントを含むかなり大きな plpgsql 関数があります。すべての if ボディ内には、stable-sql 関数への関数呼び出しがあります。

次の方法で関数を呼び出します。

SELECT * 
from rawdata.getNumbersForUserBasedMetricEventsGroupedByClient('2015-09-28','2015-10-28','{4}'::int[],2,null,null,null,null,null); 

関数の最初の 4 ～ 5 回は約2.5 秒で非常に高速に実行されますが、その後突然パフォーマンスが急速に低下し、実行に約7.5 秒かかります。連続するすべての呼び出しでそのレベルにとどまります。また、plpgsql 関数を安定していると宣言しようとしましたが、役に立ちませんでした。

内部の安定した SQL 関数の 1 つを直接呼び出すと、実行には常に約 2.5 秒かかります。

これは、rawdata.metricevent テーブルのスキーマです。

rawdata.metricevent (metriceventid bigint PRIMARY KEY,
                     metricevent integer,
                     client integer,
                     age integer,
                     country varchar(256),
                     userideventowner bigint,
                     contributoruserid bigint,
                     tournamentid bigint,
                     eventoccurtime timestamp,
                     iscounted boolean)

eventoccurtime 列に btree インデックスがあります。btree インデックスがない場合、違いはさらに大きく、実行は数秒で終了することもあれば、100 秒以上続くこともあります。

ここで私たちの質問は次のとおりです。それはなぜですか? plpgsql 関数を 5 回目または 6 回目に実行したときに、突然時間がかかるのはなぜですか? ところで、このクエリでは CPU 負荷も非常に高くなります。また、EXPLAIN ANALYZE でクエリを分析したところ、クエリ プランナーは ALWAYS で約 0.034 ミリ秒かかりましたが、クエリの実行は 2.5 秒から 7.5 秒まで異なります。また、2.5 秒または 7.5 秒のいずれかの間にあることもありません。

これらは、可変実行時間を持つ Main-pgpsql 関数と、一定の実行時間を持つ以下の stable-sql 関数です。

CREATE OR REPLACE FUNCTION rawdata.getNumbersForUserBasedMetricEventsGroupedByClient(pFrom timestamp, pTo timestamp, pMetricEvent integer[], pTimeDomainType integer,
                                                                            pCountry varchar(100),pAgeFrom integer,pAgeTo integer,pUserlanguage varchar(50),pTournamentlanguage varchar(50))
RETURNS TABLE(dfrom timestamp, x bigint, y bigint, xx bigint, yy bigint)
AS $$
BEGIN
    IF pTimeDomainType = 1 THEN
        --hours
        RETURN QUERY
            SELECT * FROM rawdata.getNumbersForUBMetricEventsGroupedByClientPerHours(pFrom,pTo,pMetricEvent,pCountry,pAgeFrom,pAgeTo,pUserLanguage,pTournamentLanguage);
    ELSIF pTimeDomainType = 2 THEN
        --days
        RETURN QUERY
            SELECT * FROM rawdata.getNumbersForUBMetricEventsGroupedByClientPerDays(pFrom,pTo,pMetricEvent,pCountry,pAgeFrom,pAgeTo,pUserLanguage,pTournamentLanguage);

    ELSIF pTimeDomainType = 3 THEN
        --week
        RETURN QUERY
            SELECT * FROM rawdata.getNumbersForUBMetricEventsGroupedByClientPerWeeks(pFrom,pTo,pMetricEvent,pCountry,pAgeFrom,pAgeTo,pUserLanguage,pTournamentLanguage);
    ELSIF pTimeDomainType = 4 THEN
        --month
        RETURN QUERY
            SELECT * FROM rawdata.getNumbersForUBMetricEventsGroupedByClientPerMonths(pFrom,pTo,pMetricEvent,pCountry,pAgeFrom,pAgeTo,pUserLanguage,pTournamentLanguage);   
    END IF;
END;
$$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION rawdata.getNumbersForUBMetricEventsGroupedByClientPerHours(pFrom timestamp, pTo timestamp, pMetricEvent integer[],
                                                                            pCountry varchar(100),pAgeFrom integer,pAgeTo integer,pUserlanguage varchar(50),pTournamentlanguage varchar(50))
RETURNS TABLE(dfrom timestamp, x bigint, y bigint, xx bigint, yy bigint)
AS $$
        SELECT hours timedomain,count(distinct em.userideventowner) as x,count(distinct ef.userideventowner) as y,count(distinct emh.userideventowner) as xx,count(distinct efh.userideventowner) as yy
        FROM generate_series
                ( pFrom::timestamp 
                , pTo::timestamp + '23 hour'
                , '1 hour'::interval) hours
           LEFT JOIN rawdata.metricevent e1 ON e1.eventoccurtime >=pFrom 
                                       AND e1.eventoccurtime < pTo + '1 day'
                                       AND (e1.metricevent = ANY (pMetricEvent))
                                       AND (e1.country = pCountry OR pCountry is null)
                                       AND (e1.age >= pAgeFrom OR pAgeFrom is null) AND (e1.age <= pAgeTo OR pAgeTo is null)
                                       AND userideventowner >= 110
                                       AND hours = date_trunc('hour',e1.eventoccurtime)
           LEFT JOIN rawdata.userlanguage ul ON e1.userideventowner = ul.userideventowner
                                                    AND (ul.userlanguage = pUserLanguage OR pUserLanguage is null)
           LEFT JOIN rawdata.metricevent ei ON e1.metriceventid = em.metriceventid AND ei.client=1
           LEFT JOIN rawdata.metricevent ea ON e1.metriceventid = ef.metriceventid AND ea.client=2
           LEFT JOIN rawdata.metricevent ew ON e1.metriceventid = emh.metriceventid AND ew.client=3
           LEFT JOIN rawdata.metricevent eww ON e1.metriceventid = efh.metriceventid AND eww.client=4
        GROUP BY hours
        ORDER BY hours;
$$
LANGUAGE sql STABLE;

CREATE OR REPLACE FUNCTION rawdata.getNumbersForUBMetricEventsGroupedByClientPerDays(pFrom timestamp, pTo timestamp, pMetricEvent integer[],
                                                                            pCountry varchar(100),pAgeFrom integer,pAgeTo integer,pUserlanguage varchar(50),pTournamentlanguage varchar(50))
RETURNS TABLE(dfrom timestamp, x bigint, y bigint, xx bigint, yy bigint)
AS $$
        SELECT days timedomain,count(distinct em.userideventowner) as x,count(distinct ef.userideventowner) as y,count(distinct emh.userideventowner) as xx,count(distinct efh.userideventowner) as yy
        FROM generate_series
                ( pFrom::timestamp 
                , pTo::timestamp
                , '1 day'::interval) days
           LEFT JOIN rawdata.metricevent e1 ON e1.eventoccurtime >=pFrom 
                               AND e1.eventoccurtime < pTo + '1 day'
                               AND (e1.metricevent = ANY (pMetricEvent))
                               AND (e1.country = pCountry OR pCountry is null)
                               AND (e1.age >= pAgeFrom OR pAgeFrom is null) AND (e1.age <= pAgeTo OR pAgeTo is null)
                               AND userideventowner >= 110
                               AND days = date_trunc('day',e1.eventoccurtime)                          
           LEFT JOIN rawdata.userlanguage ul ON e1.userideventowner = ul.userideventowner
                                            AND (ul.userlanguage = pUserLanguage OR pUserLanguage is null)
           LEFT JOIN rawdata.metricevent ei ON e1.metriceventid = em.metriceventid AND ei.client=1
           LEFT JOIN rawdata.metricevent ea ON e1.metriceventid = ef.metriceventid AND ea.client=2
           LEFT JOIN rawdata.metricevent ew ON e1.metriceventid = emh.metriceventid AND ew.client=3
           LEFT JOIN rawdata.metricevent eww ON e1.metriceventid = efh.metriceventid AND eww.client=4
        GROUP BY days
        ORDER BY days;
$$
LANGUAGE sql STABLE;

CREATE OR REPLACE FUNCTION rawdata.getNumbersForUBMetricEventsGroupedByClientPerWeeks(pFrom timestamp, pTo timestamp, pMetricEvent integer[],
                                                                            pCountry varchar(100),pAgeFrom integer,pAgeTo integer,pUserlanguage varchar(50),pTournamentlanguage varchar(50))
RETURNS TABLE(dfrom timestamp, x bigint, y bigint, xx bigint, yy bigint)
AS $$
        SELECT min(days) timedomain,count(distinct em.userideventowner) as x,count(distinct ef.userideventowner) as y,count(distinct emh.userideventowner) as xx,count(distinct efh.userideventowner) as yy
                FROM generate_series
                        ( pFrom::timestamp 
                        , pTo::timestamp
                        , '1 day'::interval) days
                   LEFT JOIN rawdata.metricevent e1 ON e1.eventoccurtime >=pFrom 
                                       AND e1.eventoccurtime < pTo + '1 day'
                                       AND (e1.metricevent = ANY (pMetricEvent)) 
                                       AND (e1.country = pCountry OR pCountry is null)
                                       AND (e1.age >= pAgeFrom OR pAgeFrom is null) AND (e1.age <= pAgeTo OR pAgeTo is null)
                                       AND userideventowner >= 110
                                       AND days = date_trunc('day',e1.eventoccurtime)
                   LEFT JOIN rawdata.userlanguage ul ON e1.userideventowner = ul.userideventowner
                                                    AND (ul.userlanguage = pUserLanguage OR pUserLanguage is null)
                   LEFT JOIN rawdata.metricevent ei ON e1.metriceventid = em.metriceventid AND ei.client=1
                   LEFT JOIN rawdata.metricevent ea ON e1.metriceventid = ef.metriceventid AND ea.client=2
                   LEFT JOIN rawdata.metricevent ew ON e1.metriceventid = emh.metriceventid AND ew.client=3
                   LEFT JOIN rawdata.metricevent eww ON e1.metriceventid = efh.metriceventid AND eww.client=4
                GROUP BY EXTRACT(WEEK FROM days)
                ORDER BY 1;
$$
LANGUAGE sql STABLE;

CREATE OR REPLACE FUNCTION rawdata.getNumbersForUBMetricEventsGroupedByClientPerMonths(pFrom timestamp, pTo timestamp, pMetricEvent integer[],
                                                                            pCountry varchar(100),pAgeFrom integer,pAgeTo integer,pUserlanguage varchar(50),pTournamentlanguage varchar(50))
RETURNS TABLE(dfrom timestamp, x bigint, y bigint, xx bigint, yy bigint)
AS $$
        SELECT min(days) timedomain,count(distinct em.userideventowner) as x,count(distinct ef.userideventowner) as y,count(distinct emh.userideventowner) as xx,count(distinct efh.userideventowner) as yy
                FROM generate_series
                        ( pFrom::timestamp 
                        , pTo::timestamp
                        , '1 day'::interval) days
                   LEFT JOIN rawdata.metricevent e1 ON e1.eventoccurtime >=pFrom 
                                       AND e1.eventoccurtime < pTo + '1 day'
                                       AND (e1.metricevent = ANY (pMetricEvent)) 
                                       AND (e1.country = pCountry OR pCountry is null)
                                       AND (e1.age >= pAgeFrom OR pAgeFrom is null) AND (e1.age <= pAgeTo OR pAgeTo is null)
                                       AND userideventowner >= 110
                                       AND days = date_trunc('day',e1.eventoccurtime)
                   LEFT JOIN rawdata.userlanguage ul ON e1.userideventowner = ul.userideventowner
                                                    AND (ul.userlanguage = pUserLanguage OR pUserLanguage is null)LEFT JOIN rawdata.metricevent ei ON e1.metriceventid = em.metriceventid AND ei.client=1
                   LEFT JOIN rawdata.metricevent ea ON e1.metriceventid = ef.metriceventid AND ea.client=2
                   LEFT JOIN rawdata.metricevent ew ON e1.metriceventid = emh.metriceventid AND ew.client=3
                   LEFT JOIN rawdata.metricevent eww ON e1.metriceventid = efh.metriceventid AND eww.client=4
                GROUP BY EXTRACT(MONTH FROM days)
                ORDER BY 1;         
$$
LANGUAGE sql STABLE;

よろしく、 トーマス