{"id":75678,"date":"2020-03-27T19:42:27","date_gmt":"2020-03-27T17:42:27","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/o-chem-molchit-explain-i-kak-ego-razgovorit"},"modified":"2020-03-27T19:42:27","modified_gmt":"2020-03-27T17:42:27","slug":"o-chem-molchit-explain-i-kak-ego-razgovorit","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hu\/blog\/administrirovanie\/o-chem-molchit-explain-i-kak-ego-razgovorit","title":{"rendered":"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>A klasszikus k\u00e9rd\u00e9s, amellyel a fejleszt\u0151 a DBA-j\u00e1hoz vagy a PostgreSQL tan\u00e1csad\u00f3j\u00e1hoz fordul, szinte mindig ugyan\u00fagy hangzik: <i>\u201eMi\u00e9rt tart olyan sok\u00e1ig a lek\u00e9rdez\u00e9sek v\u00e9grehajt\u00e1sa?\u201d<\/i><\/p>\n<p>Hagyom\u00e1nyos okok halmaza:<\/p>\n<ul>\n<li><b>hat\u00e9konytalan algoritmus<\/b><br \/>\namikor \u00fagy d\u00f6nt\u00f6tt, hogy JOIN-t v\u00e9gez t\u00f6bb CTE-vel n\u00e9h\u00e1ny t\u00edzezer rekord eset\u00e9n<\/li>\n<li><b>elavult statisztik\u00e1k<\/b><br \/>\nha az adatok t\u00e9nyleges eloszl\u00e1sa a t\u00e1bl\u00e1zatban m\u00e1r jelent\u0151sen elt\u00e9r az ANALYZE \u00e1ltal legut\u00f3bb gy\u0171jt\u00f6tt\u0151l<\/li>\n<li><b>\u201eelakad\u00e1s\u201d az er\u0151forr\u00e1sokban<\/b><br \/>\n\u00e9s m\u00e1r nem elegend\u0151ek a kiosztott CPU sz\u00e1m\u00edt\u00e1si kapacit\u00e1sai, folyamatosan megn\u00f6vekszik a mem\u00f3riahaszn\u00e1lat vagy a lemez nem tud l\u00e9p\u00e9st tartani az adatb\u00e1zis minden \u201ek\u00edv\u00e1ns\u00e1g\u00e1val\u201d<\/li>\n<li><b>z\u00e1rol\u00e1sok<\/b> a verseng\u0151 folyamatok \u00e1ltal<\/li>\n<\/ul>\n<p>\n\u00c9s ha a z\u00e1rol\u00e1sok meglehet\u0151sen nehezen megfoghat\u00f3k \u00e9s elemezhet\u0151k, akkor a t\u00f6bbihez el\u00e9g nek\u00fcnk <b>lek\u00e9rdez\u00e9si terv<\/b>, amit a k\u00f6vetkez\u0151vel szerezhet\u00fcnk be: <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/using-explain\">EXPLAIN utas\u00edt\u00e1s<\/a><\/noindex> (<i>term\u00e9szetesen a legjobb, ha azonnal EXPLAIN (ANALYZE, BUFFERS) \u2026<\/i>) vagy <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/auto-explain\">az auto_explain modul<\/a><\/noindex>.<\/p>\n<p>De, ahogy a dokument\u00e1ci\u00f3ban is mondj\u00e1k, <\/p>\n<blockquote><p>\u201eA terv meg\u00e9rt\u00e9se m\u0171v\u00e9szet, \u00e9s annak elsaj\u00e1t\u00edt\u00e1s\u00e1hoz bizonyos tapasztalat sz\u00fcks\u00e9ges, \u2026\u201d<\/p><\/blockquote>\n<p> De n\u00e9lk\u00fcle is megoldhat\u00f3, ha egy megfelel\u0151 eszk\u00f6zt haszn\u00e1lunk!<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><br \/>\nHogyan n\u00e9z ki \u00e1ltal\u00e1ban a lek\u00e9rdez\u00e9si terv? Valahogy \u00edgy:<\/p>\n<pre><code class=\"plaintext\">Index Scan using pg_class_relname_nsp_index on pg_class (actual time=0.049..0.050 rows=1 loops=1)\n  Index Cond: (relname = $1)\n  Filter: (oid = $0)\n  Buffers: shared hit=4\n  InitPlan 1 (returns $0,$1)\n    -&gt;  Limit (actual time=0.019..0.020 rows=1 loops=1)\n          Buffers: shared hit=1\n          -&gt;  Seq Scan on pg_class pg_class_1 (actual time=0.015..0.015 rows=1 loops=1)\n                Filter: (relkind = 'r'::&quot;char&quot;)\n                Rows Removed by Filter: 5\n                Buffers: shared hit=1<\/code><\/pre>\n<p>\nvagy \u00edgy:<\/p>\n<pre><code class=\"plaintext\">&quot;Append  (cost=868.60..878.95 rows=2 width=233) (actual time=0.024..0.144 rows=2 loops=1)&quot;\n&quot;  Buffers: shared hit=3&quot;\n&quot;  CTE cl&quot;\n&quot;    -&gt;  Seq Scan on pg_class  (cost=0.00..868.60 rows=9972 width=537) (actual time=0.016..0.042 rows=101 loops=1)&quot;\n&quot;          Buffers: shared hit=3&quot;\n&quot;  -&gt;  Limit  (cost=0.00..0.10 rows=1 width=233) (actual time=0.023..0.024 rows=1 loops=1)&quot;\n&quot;        Buffers: shared hit=1&quot;\n&quot;        -&gt;  CTE Scan on cl  (cost=0.00..997.20 rows=9972 width=233) (actual time=0.021..0.021 rows=1 loops=1)&quot;\n&quot;              Buffers: shared hit=1&quot;\n&quot;  -&gt;  Limit  (cost=10.00..10.10 rows=1 width=233) (actual time=0.117..0.118 rows=1 loops=1)&quot;\n&quot;        Buffers: shared hit=2&quot;\n&quot;        -&gt;  CTE Scan on cl cl_1  (cost=0.00..997.20 rows=9972 width=233) (actual time=0.001..0.104 rows=101 loops=1)&quot;\n&quot;              Buffers: shared hit=2&quot;\n&quot;Planning Time: 0.634 ms&quot;\n&quot;Execution Time: 0.248 ms&quot;<\/code><\/pre>\n<p>\nDe a tervet \u201epap\u00edrr\u00f3l\u201d olvasni nagyon neh\u00e9z \u00e9s nem szeml\u00e9letes:<\/p>\n<ul>\n<li>a csom\u00f3pontban megjelenik <b>az er\u0151forr\u00e1sok \u00f6sszess\u00e9ge az als\u00f3 f\u00e1ban<\/b><br \/>\nteh\u00e1t ahhoz, hogy meg\u00e9rts\u00fck, mennyi id\u0151 telt el egy adott csom\u00f3pont v\u00e9grehajt\u00e1s\u00e1ra, vagy hogy pontosan mennyi id\u0151t vett ig\u00e9nybe az adatok leolvas\u00e1sa a t\u00e1bl\u00e1zatb\u00f3l \u2014 valahogy ki kell vonnunk az egyiket a m\u00e1sikb\u00f3l<\/li>\n<li>sz\u00fcks\u00e9g van a csom\u00f3pont id\u0151re <b>szorozni a loops-szal<\/b><br \/>\nigen, a kivon\u00e1s m\u00e9g nem a legnehezebb m\u0171velet, amit \"fejben\" el kell v\u00e9gezni \u2014 hiszen a v\u00e9grehajt\u00e1si id\u0151 az egy v\u00e9grehajt\u00e1sra vonatkoz\u00f3 \u00e1tlagolt id\u0151t mutat, \u00e9s ezekb\u0151l t\u00f6bb sz\u00e1z is lehet<\/li>\n<li>nos, \u00e9s mindez egy\u00fctt megnehez\u00edti a f\u0151 k\u00e9rd\u00e9s megv\u00e1laszol\u00e1s\u00e1t \u2014 ki is a leggyeng\u00e9bb l\u00e1ncszem <b>a \"leggyeng\u00e9bb l\u00e1ncszem\"<\/b>?<\/li>\n<\/ul>\n<p>\nAmikor megpr\u00f3b\u00e1ltuk mindezt elmagyar\u00e1zni n\u00e9h\u00e1ny sz\u00e1z fejleszt\u0151nknek, r\u00e1j\u00f6tt\u00fcnk, hogy k\u00edv\u00fclr\u0151l ez k\u00f6r\u00fclbel\u00fcl \u00edgy n\u00e9z ki:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/abb07e902639b5ec245851aa4a0edb58.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nAkkor teh\u00e1t sz\u00fcks\u00e9g\u00fcnk van\u2026<\/p>\n<h2>Eszk\u00f6z<\/h2>\n<p>\nEbben pr\u00f3b\u00e1ltunk \u00f6sszegy\u0171jteni minden kulcsmechanik\u00e1t, amely seg\u00edt a terv \u00e9s a k\u00e9r\u00e9s alapj\u00e1n meg\u00e9rteni, \"ki a felel\u0151s \u00e9s mit kell tenni\". Nos, \u00e9s a tapasztalatunk egy r\u00e9sz\u00e9t is megosztani az k\u00f6z\u00f6ss\u00e9ggel.<br \/>\nItt az ideje, hogy megismerd \u00e9s haszn\u00e1ld \u2014 <noindex><a rel=\"nofollow\" href=\"https:\/\/explain.tensor.ru\/\">explain.tensor.hu<\/a><\/noindex> <\/p>\n<h3>A tervek \u00e1ttekinthet\u0151s\u00e9ge<\/h3>\n<p>\nK\u00f6nny\u0171 meg\u00e9rteni a tervet, amikor \u00edgy n\u00e9z ki?<\/p>\n<pre><code class=\"plaintext\">Seq Scan on pg_class (aktualiz\u00e1lt id\u0151=0.009..1.304 sor=6609 ciklus=1)\n  Pufferek: megosztott tal\u00e1lat=263\n Tervez\u00e9si id\u0151: 0.108 ms\n V\u00e9grehajt\u00e1si id\u0151: 1.800 ms\n<\/code><\/pre>\n<p>\nNem igaz\u00e1n.<\/p>\n<p>De \u00edgy, <b>r\u00f6vid\u00edtett form\u00e1ban<\/b>, amikor a kulcsfontoss\u00e1g\u00fa mutat\u00f3k elk\u00fcl\u00f6n\u00edtve vannak \u2014 m\u00e1r sokkal \u00e9rthet\u0151bb:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/18404ce800de847f1934ac2c7fef10be.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nDe ha a terv bonyolultabb \u2014 seg\u00edts\u00e9get ny\u00fajt <b>a piechart a t\u00f6lt\u00f6tt id\u0151 eloszl\u00e1s\u00e1r\u00f3l<\/b> a csom\u00f3pontok szerint:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/ca9fdd07278801e4f3ad15e997efc1a0.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nNos, a legbonyolultabb esetekhez seg\u00edts\u00e9g\u00fcl siet <b>a v\u00e9grehajt\u00e1si diagram<\/b>:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/c03f358858206d7ccae20fd8142baa8c.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nP\u00e9ld\u00e1ul vannak olyan el\u00e9g nem trivi\u00e1lis helyzetek, amikor a terv t\u00f6bb t\u00e9nyleges gy\u00f6k\u00e9rrel rendelkezhet:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/ea4f3f498737e9cc3f8f40c16a5bd1d7.png\" style=\"display:block;margin: 0 auto;\" \/><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/267273e8491d6b4403442672612c33ff.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<\/p>\n<h3>Struktur\u00e1lt tippek<\/h3>\n<p>\nNos, ha a terv teljes szerkezete \u00e9s a gyenge pontjai m\u00e1r ki vannak dolgozva \u00e9s l\u00e1that\u00f3ak \u2014 mi\u00e9rt ne emelhetn\u00e9nk ki \u0151ket a fejleszt\u0151nek, \u00e9s magyar\u00e1zhatn\u00e1nk \"anyanyelvi\" \u00e9rthet\u0151s\u00e9ggel?<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/0e7157a09f7f5707e769cc1d6a8f3af8.png\" style=\"display:block;margin: 0 auto;\" \/>Ezekb\u0151l a javaslati sablonokb\u00f3l m\u00e1r \u00f6sszegy\u0171jt\u00f6tt\u00fcnk n\u00e9h\u00e1ny tucatot.<\/p>\n<h3>Sor szerinti lek\u00e9rdez\u00e9sprofil\u00e1l\u00f3<\/h3>\n<p>\nMost, ha az elemzett tervhez hozz\u00e1csatolj\u00e1k az eredeti lek\u00e9rdez\u00e9st, l\u00e1that\u00f3, mennyi id\u0151t t\u00f6lt\u00f6ttek el egyes oper\u00e1torokkal \u2014 k\u00f6r\u00fclbel\u00fcl \u00edgy:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/0766d331798d529363d10006ace211f3.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\n\u2026 vagy ak\u00e1r \u00edgy:<\/p>\n<p><img decoding=\"async\" alt=\"Mir\u0151l hallgat az EXPLAIN, \u00e9s hogyan lehet besz\u00e9lget\u00e9sre b\u00edrni\" src=\"\/wp-content\/uploads\/2020\/03\/4efd23d84792c5a7f54b40e86ff17353.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<\/p>\n<h3>Param\u00e9terek behelyettes\u00edt\u00e9se a lek\u00e9rdez\u00e9sbe<\/h3>\n<p>\nHa \"hozz\u00e1kapcsoltad\" a tervhez nemcsak a lek\u00e9rdez\u00e9st, hanem annak param\u00e9tereit is a log DETAIL sor\u00e1b\u00f3l, akkor egy kib\u0151v\u00edtett form\u00e1ban lem\u00e1solhatod:<\/p>\n<ul>\n<li>\u00e9rt\u00e9kek behelyettes\u00edt\u00e9se a lek\u00e9rdez\u00e9sbe<br \/>\nk\u00f6zvetlen v\u00e9grehajt\u00e1s c\u00e9lj\u00e1b\u00f3l a saj\u00e1t adatb\u00e1zisodon \u00e9s tov\u00e1bbi profiloz\u00e1sra<\/p>\n<pre><code class=\"sql\">SELECT 'const', 'param'::text;<\/code><\/pre>\n<\/li>\n<li>\u00e9rt\u00e9kek behelyettes\u00edt\u00e9se a PREPARE\/EXECUTE seg\u00edts\u00e9g\u00e9vel<br \/>\na feladatkezel\u0151 m\u0171k\u00f6d\u00e9s\u00e9nek szimul\u00e1l\u00e1s\u00e1ra, amikor a param\u00e9teres r\u00e9sz figyelmen k\u00edv\u00fcl hagyhat\u00f3 \u2014 p\u00e9ld\u00e1ul, ha szegment\u00e1lt t\u00e1bl\u00e1kon dolgozunk<\/p>\n<pre><code class=\"sql\">DEALLOCATE ALL;\nPREPARE q(text) AS SELECT 'const', $1::text;\nEXECUTE q('param'::text);\n<\/code><\/pre>\n<\/li>\n<\/ul>\n<p><\/p>\n<h3>Tervezetek arch\u00edvuma<\/h3>\n<p>\nIllessze be, elemezze, ossza meg koll\u00e9g\u00e1ival! A tervek az arch\u00edvumban maradnak, \u00e9s k\u00e9s\u0151bb visszat\u00e9rhet hozz\u00e1juk: <noindex><a rel=\"nofollow\" href=\"https:\/\/explain.tensor.ru\/archive\/\">explain.tensor.hu\/archive<\/a><\/noindex><\/p>\n<p>De ha nem szeretn\u00e9, hogy m\u00e1sok l\u00e1ss\u00e1k a terv\u00e9t, ne felejtse el bejel\u00f6lni a \u201ene tegy\u00fck k\u00f6zz\u00e9 az arch\u00edvumban\u201d lehet\u0151s\u00e9get.<\/p>\n<p>A k\u00f6vetkez\u0151 cikkekben besz\u00e9lek azokr\u00f3l a neh\u00e9zs\u00e9gekr\u0151l \u00e9s megold\u00e1sokr\u00f3l, amelyek az elemz\u00e9si tervvel kapcsolatban mer\u00fclnek fel.<br \/>\n<br \/>Forr\u00e1s: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/company\/tensor\/blog\/477624\/\">habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u041a\u043b\u0430\u0441\u0441\u0438\u0447\u0435\u0441\u043a\u0438\u0439 \u0432\u043e\u043f\u0440\u043e\u0441, \u0441 \u043a\u043e\u0442\u043e\u0440\u044b\u043c \u0440\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a \u043f\u0440\u0438\u0445\u043e\u0434\u0438\u0442 \u043a \u0441\u0432\u043e\u0435\u043c\u0443 DBA \u0438\u043b\u0438 \u0432\u043b\u0430\u0434\u0435\u043b\u0435\u0446 \u0431\u0438\u0437\u043d\u0435\u0441\u0430 \u2014 \u043a \u043a\u043e\u043d\u0441\u0443\u043b\u044c\u0442\u0430\u043d\u0442\u0443 \u043f\u043e PostgreSQL, \u043f\u043e\u0447\u0442\u0438 \u0432\u0441\u0435\u0433\u0434\u0430 \u0437\u0432\u0443\u0447\u0438\u0442 \u043e\u0434\u0438\u043d\u0430\u043a\u043e\u0432\u043e: \u00ab\u041f\u043e\u0447\u0435\u043c\u0443 \u0437\u0430\u043f\u0440\u043e\u0441\u044b \u0432\u044b\u043f\u043e\u043b\u043d\u044f\u044e\u0442\u0441\u044f \u043d\u0430 \u0431\u0430\u0437\u0435 \u0442\u0430\u043a \u0434\u043e\u043b\u0433\u043e?\u00bb \u0422\u0440\u0430\u0434\u0438\u0446\u0438\u043e\u043d\u043d\u044b\u0439 \u043d\u0430\u0431\u043e\u0440 \u043f\u0440\u0438\u0447\u0438\u043d: \u043d\u0435\u044d\u0444\u0444\u0435\u043a\u0442\u0438\u0432\u043d\u044b\u0439 \u0430\u043b\u0433\u043e\u0440\u0438\u0442\u043c \u043a\u043e\u0433\u0434\u0430 \u0432\u044b \u0440\u0435\u0448\u0438\u043b\u0438 \u0441\u0434\u0435\u043b\u0430\u0442\u044c JOIN \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u0438\u0445 CTE \u043f\u043e \u043f\u0430\u0440\u0435 \u0434\u0435\u0441\u044f\u0442\u043a\u043e\u0432 \u0442\u044b\u0441\u044f\u0447 \u0437\u0430\u043f\u0438\u0441\u0435\u0439 \u043d\u0435\u0430\u043a\u0442\u0443\u0430\u043b\u044c\u043d\u0430\u044f \u0441\u0442\u0430\u0442\u0438\u0441\u0442\u0438\u043a\u0430 \u0435\u0441\u043b\u0438 \u0444\u0430\u043a\u0442\u0438\u0447\u0435\u0441\u043a\u043e\u0435 \u0440\u0430\u0441\u043f\u0440\u0435\u0434\u0435\u043b\u0435\u043d\u0438\u0435 \u0434\u0430\u043d\u043d\u044b\u0445 \u0432 \u0442\u0430\u0431\u043b\u0438\u0446\u0435 \u0443\u0436\u0435 \u0441\u0438\u043b\u044c\u043d\u043e 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