人如其名 (人如其名) 2023 年5 月 28 日 05:07 6 我感觉这是统计缺陷,算子在执行过程中有三个步骤(经典火山模型):open、next、close。IndexReader在统计执行时间时候是在next时候统计的。但是去tikv请求数据时候是在open阶段就开始了,但是并没有统计到IndexReader里面。如果大结果集执行时间大多都在Next上的时候...
PostgreSQL uses a Least Recently Used (LRU) cache to store frequently used data in memory. Buffers display how much of the data comes from a cache, and how much is retrieved from disk. Displays the number of shared, local, and temp blocks hits, reads, and writes. The data provided by...
it works well for concurrent applications and scales to any number of processors. It even optimizes the memory layout with respect to the CPU caches to improve[cache locality]and avoid[false sharing].
If the duration is long, the cache may not be hit. Create split reader cost: the duration that is taken to open a file. If the duration is long, the metadata of the file does not hit the cache. If this occurs, the I/O overhead is high. Get result cost: the duration from ...
copr_cache_hit_ratio: 0.62, distsql_concurrency: 15} | data:TableFullScan_24 | 58.6 MB | N/A | | └─TableFullScan_24 | 90000.00 | 90000 | cop[tikv] | table:t2 | tikv_task:{proc max:31ms, min:0s, avg: 13ms, p80:19ms, p95:26ms, iters:181, tasks:24}, scan_detail: ...
Sorts are expensive operations especially on large tables where the rows do not fit in memory and spill to disk. By default sort blocks are placed into the buffer cache. This may result in aging out of other blocks that may be reread by other processes. To avoid this you can use the pa...
由于数据压缩比更好,一方面节省了磁盘空间,另一方面对于cache也有了更大的发挥空间 DBMS的功能:几乎覆盖了标准SQL的大部分语法,包括DDL和DML,以及配套的各种函数,用户管理及权限管理,数据的备份与恢复; 多样化引擎:ClickHouse和MySQL类似,把表级的存储引擎插件化,根据表的不同需求可以设定不同的存储引擎。目前包括合并树...
| Source:PLAN_CACHE | | TemplateId: 5819c807 EXPLAIN EXECUTE语句:表示下推SQL在MySQL的执行情况,这个语句和MySQL的explain语句同义。通过该语句可以查看下推SQL在DN上有没有使用索引,有没有做全表扫描。 EXPLAINEXECUTEselect count(*) from lineitem group byL_ORDERKEY; ...
In-memory package cache Package cache event monitor name The procedure searches for the section in the given location. An executable ID uniquely and consistently identifies a section. The executable ID is an opaque, binary token generated at the data server for each section that has been executed...
ByteByteGoHq / system-design-101 Public Notifications You must be signed in to change notification settings Fork 7.3k Star 69.1k Explain complex systems using visuals and simple terms. Help you prepare for system design interviews.