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\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"返回結果如下圖所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/43\/f1\/43f14146a075b8a09417b34ec1abyyf1.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"從上圖中可以看到test表中返回了一條partitionid爲20210301的數據分區的記錄，從name字段中我們可以得知，此分區的目錄名爲20210301_8_8_0。20210301_8_8_0這個目錄名字到底有什麼含義呢？下面來介紹一下分區規則以及分區目錄的命名規則。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.1 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00:00:00'));\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因爲index_granularity設置爲4，所以每4條數據就會生成一條索引記錄，即使用插入的第1、5、9條數據id字段的值生成索引文件記錄。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/d6\/9c\/d6ef6c6d12d669a97b0940e852caf29c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.3.3 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ClickHouse核心引擎MergeTree解讀
{"type":"doc","content":[{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"ClickHouse"},{"type":"text","text":" 是俄羅斯最大的搜索引擎Yandex在2016年開源的數據庫管理系統（DBMS），主要用於聯機分析處理（OLAP）。其採用了面向列的存儲方式，性能遠超傳統面向行的DBMS，近幾年受到廣泛關注。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文將介紹 "},{"type":"text","marks":[{"type":"strong"}],"text":"ClickHouse MergeTree系列表引擎"},{"type":"text","text":" 的相關知識，並通過示例分析MergeTree存儲引擎的數據存儲結構。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"1 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當合並數據時，會把具有相同主鍵的記錄合併爲一條記錄。根據聚合字段設置，該字段的值爲聚合後的彙總值，非聚合字段使用第一條記錄的值，聚合字段類型必須爲數值類型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"AggregatingMergeTree"},{"type":"text","text":"： 在同一數據分區下，可以將具有相同主鍵的數據進行聚合。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"CollapsingMergeTree"},{"type":"text","text":"： 在同一數據分區下，對具有相同主鍵的數據進行摺疊合併。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"VersionedCollapsingMergeTree"},{"type":"text","text":"："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"基於CollapsingMergeTree引擎，增添了數據版本信息字段配置選項。在數據依據ORDER BY設置對數據進行排序的基礎上，如果數據的版本信息列不在排序字段中，那麼版本信息會被隱式的作爲ORDER BY的最後一列從而影響數據排序。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"GraphiteMergeTree"},{"type":"text","text":"： 用來存儲時序數據庫Graphites的數據。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MergeTree是該系列引擎中最核心的引擎，其他引擎均以MergeTree爲基礎，並在數據合併過程中實現了不同的特性，從而構成了MergeTree表引擎家族。下面我們通過MergeTree來具體瞭解MergeTree表系列引擎。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"2 MergeTree引擎"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.1 表創建"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"創建MergeTree的DDL如下所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster] \n(\n name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [TTL expr1], \n name2 [type2] 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：分區鍵，指明表中的數據以何種規則進行分區。分區是在一個表中通過指定的規則劃分而成的邏輯數據集。分區可以按任意標準進行，如按月、按日或按事件類型。爲了減少需要操作的數據，每個分區都是分開存儲的。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"PRIMARY KEY"},{"type":"text","text":" ：主鍵，設置後會按照主鍵生成一級索引（primary.idx），數據會依據索引的設置進行排序，從而加速查詢性能。默認情況下，PRIMARY KEY與ORDER BY設置相同，所以通常情況下直接使用ORDER BY設置來替代主鍵設置。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"SAMPLE BY"},{"type":"text","text":" ：數據採樣設置，如果顯示配置了該選項，那麼主鍵配置中也應該包括此配置。例如 ORDER BY CounterID \/ EventDate \/ intHash32（UserID）、SAMPLE BY 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：索引間隔粒度。MergeTree索引爲稀疏索引，每index_granularity個數據產生一條索引。index_granularity默認設置爲8092。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"enable_mixed_granularity_parts"},{"type":"text","text":" ：是否啓動index_granularity_bytes來控制索引粒度大小。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"index_granularity_bytes"},{"type":"text","text":" ：索引粒度，以字節爲單位，默認10Mb。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"merge_max_block_size"},{"type":"text","text":" ：數據塊合併最大記錄個數，默認8192。"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"merge_with_ttl_timeout"},{"type":"text","text":" ：合併頻率最小時間間隔，默認1天。"}]}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.2 數據存儲結構"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先創建一個test表，DDL如下:"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"CREATE TABLE test.test \n( \n id UInt64, \n type UInt8, \n create_time DateTime \n) ENGINE = MergeTree() \n PARTITION BY toYYYYMMDD(create_time) \n ORDER BY (id) \n SETTINGS index_granularity = 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\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"返回結果如下圖所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/43\/f1\/43f14146a075b8a09417b34ec1abyyf1.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"從上圖中可以看到test表中返回了一條partitionid爲20210301的數據分區的記錄，從name字段中我們可以得知，此分區的目錄名爲20210301_8_8_0。20210301_8_8_0這個目錄名字到底有什麼含義呢？下面來介紹一下分區規則以及分區目錄的命名規則。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.2.1 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數據文件"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MergeTree中，每列都對應一個bin文件單獨存放該列數據。例如，id.bin存放的是id列的數據。所有數據都經過數據壓縮、排序，最後以數據塊的形式寫入bin文件中。bin中數據以壓縮數據塊爲單位寫入文件中。每個數據塊由頭信息和壓縮數據組成。頭部信息包括校驗和、數據壓縮算法、數據壓縮前大小和壓縮後大小組成。壓縮數據由granule組成，granule大小與index_granularity相關。"}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.3.2 索引文件"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MergeTree索引爲稀疏索引，它並不索引單條數據，而是索引一定範圍的數據。也就是從已排序的全量數據中，間隔性的選取一些數據記錄主鍵字段的值來生成primary.idx索引文件，從而加快表查詢效率。間隔設置參數爲index_granularity。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/bb\/4c\/bbc302f044278bbfcc3c16d63f15a34c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們向表test中插入9條數據，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"insert into test.test(id, type, create_time) VALUES (1, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (1, 2, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (1, 3, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (2, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (2, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (3, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (3, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (4, 1, toDateTime('2021-03-01 00:00:00')); \ninsert into test.test(id, type, create_time) VALUES (5, 1, toDateTime('2021-03-01 00:00:00'));\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因爲index_granularity設置爲4，所以每4條數據就會生成一條索引記錄，即使用插入的第1、5、9條數據id字段的值生成索引文件記錄。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/d6\/9c\/d6ef6c6d12d669a97b0940e852caf29c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.3.3 標記文件"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"mrk標記文件在primary.idx索引文件和bin數據文件之間起到了橋樑作用。primary.idx文件中的每條索引在mrk文件中都有對應的一條記錄。一條記錄的組成包括："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"offset-compressed bin file"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"表示指向的壓縮數據塊在bin文件中的偏移量。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"offset-decompressed data block"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"表示指向的數據在解壓數據塊中的偏移量。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"row counts"}]}]},{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"代表數據記錄行數，小於等於index_granularity所設置的值。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/57\/d6\/57c2c50d02c4bf7637007fb3b337d6d6.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"索引，標記和數據文件下圖所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/b2\/85\/b2dabc9da1d48abca91627a46c08dd85.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"作者：TalkingData 張凱"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"參考文檔："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.https:\/\/clickhouse.tech\/docs"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.http:\/\/www.clickhouse.com.cn\/topic\/5ffec51eba8f16b55dd0ffe4"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.《ClickHouse原理解析與應用實踐》（機械工業出版社出版，作者朱凱）"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"本文轉載自公衆號TalkingData（ID：Talkingdata）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"原文鏈接"},{"type":"text","text":"："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https:\/\/mp.weixin.qq.com\/s\/YWSmRqOOC3F5KeDBPg2g1A","title":"","type":null},"content":[{"type":"text","text":"ClickHouse核心引擎MergeTree解讀"}]}]}]}
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