Query Evaluation 2 It is sometimes necessary or useful to sort data as it is scanned (read) The cost to scan a file is B(R) ▪ To satisfy a query with an ORDER BY clause ▪ Or because an algorithm requires sorted input ▪ Such as projection or some join algorithms There are […]
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CMPT 454 A traditional database requires both persistent and working (transient) memory ▪ The data is stored in non-volatile secondary storage to reduce the risk of data loss ▪ Hard Disk Drive (HDD) or Solid State Drive (SSD) ▪ Data is transferred from disk to main memory ▪ Where operations (read, update, write, …)
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Improving HDD Efficiency and Reliability Hard disks act as bottlenecks for processing ▪ DB data is stored on disks, and must be fetched into main memory to be processed ▪ Disk access is considerably slower than main memory processing Hard disks are also relatively unreliable ▪ Disks contain mechanical components that are more
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Query Evaluation 3 Projections Nested Loop Joins John Edgar 2 3.1 Naively, projection and duplicate removal entails ▪ Scan the table, remove unwanted attributes, and write it back SELECT DISTINCT fname, lname FROM Customer ▪ cost 2B disk I/Os ▪ cost 4B, possibly more if the file is very large
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Structure and Insertion Multiple level indexes can be very useful in speeding up queries ▪ B and B+ trees are used in commercial DBMSs B trees have two desirable properties ▪ They are multiple level indexes ▪ Maintain as many levels as are required for the file being indexed ▪ The number of
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Carnegie Mellon Linking 15-213/18-213/15-513: Introduction to Computer Systems 14th Lecture, July 1, 2020 Bryant and O’Hallaron, Computer Systems: A Programmer’s Perspective, Third Edition 1 Carnegie Mellon Today Linking ▪ Motivation ▪ What it does ▪ How it works ▪ Dynamic linking Case study: Library interpositioning Bryant and O’Hallaron, Computer Systems: A Programmer’s Perspective,
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Skiplists, Bitmap Indices, kd Trees Skiplist Bitmap Indexes kd Trees 5.1 B and B+ trees are the most commonly used ordered DBMS index structure ▪ Tree nodes are mapped to disk pages In-memory DBs allows the use of other index structures ▪ That do not have to be optimized for
Carnegie Mellon Code Optimization 15-213/18-213/15-513: Introduction to Computer Systems 13th Lecture, June 17, 2020 Bryant and O’Hallaron, Computer Systems: A Programmer’s Perspective, Third Edition 1 Carnegie Mellon Rear Admiral Grace Hopper ▪ Invented first compiler in 1951 (technically it was a linker) ▪ Coined “compiler” (and “bug”) ▪ Compiled for Harvard Mark I ▪
Query Evaluation 1 Introduction Metrics Unary Operators John Edgar 2 select c.cid, c.cname, c.email, p.pid, p.pname, p.price from customer c, sales s, product p where c.city = ‘Vancouver’ and p.company = ‘lego’ and s.year = 2019 and s.cid = c.cid and s.pid = p.pid SQL is procedural Operations are specified select c.cid,
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And SSDs Buffer management Solid State Drives John Edgar 2 5.1 Main memory is partitioned into a collection of frames called the buffer pool ▪ The buffer manager is responsible for bringing pages from disk to main memory as required ▪ Pages are mapped to frames ▪ Processes inform the buffer manager
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