[SOLVED] CS database Storage Management

Storage Management

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Storage Management

Storage Management

Storage Technology

Views of Data in Query Evaluation

Storage Management

Cost Models

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Storage Management

Lowest levels of DBMS related to storage management:

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Storage Technology

Persistent storage is

large, cheap, relatively slow, accessed in blocks

used for long-term storage of data

Computational storage is
small, expensive, fast, accessed by byte/word

used for all analysis of data

Access cost HDD:RAM 100000:1, e.g.
10ms to read block containing two tuples

1s to compare fields in two tuples

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Storage Technology (cont)

Hard disk drives (HDD) are well-established, cheap, high-volume,

spinning magnetic medium

access requires moving r/w head to position

transfers blocks of data (e.g. 1KB)

Latency: move to track + spin to block = ~10ms (avg)

Volume: one HDD can store up to 20TB (typically 4TB/8TB/)

Summary: very large, persistent, slow, block-based transfer

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Storage Technology (cont)

Solid state drives (SSD) are modern, high-volume devices

faster than HDDs, no latency

can read single items

update requires block erase then write

over time, writes wear out blocks

require controllers that spread write load

Volume: one SSD can store up to 8TB (typically 1TB/2TB/)

Summary: large, persistent, fast, (partly) block-based transfer

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Storage Technology (cont)

Comparison of storage device properties:

RAMHDDSDD
Capacity~ 32GB~ 8TB~ 2TB
Cost/byte~ $10 / GB~ $40 / TB~ $200 / TB
Read latency~ 1s~ 10ms~ 50s
Write latency~ 1s~ 10ms~ 900s
Read unitbyteblock (e.g. 1KB)byte
Writingbytewrite a blockwrite on empty block

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Storage Technology (cont)

Aims of storage management in DBMS:

provide view of data as collection of pages/tuples

map from database objects (e.g. tables) to disk files

manage transfer of data to/from disk storage

use buffers to minimise disk/memory transfers

interpret loaded data as tuples/records

basis for file structures used by access methods

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Views of Data in Query Evaluation

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Views of Data in Query Evaluation (cont)

Representing database objects during query execution:

DB (handle on an authorised/opened database)

Rel (handle on an opened relation)

Page (memory buffer to hold contents of disk block)

Tuple (memory holding data values from one tuple)

Addressing in DBMSs:
PageID = FileID+Offset identifies a block of data
where Offset gives location of block within file

TupleID = PageID+Index identifies a single tuple
where Index gives location of tuple within page

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Storage Management

Topics in storage management

Disks and Files
performance issues and organisation of disk files

Buffer Management
using caching to improve DBMS system throughput

Tuple/Page Management
how tuples are represented within disk pages

DB Object Management (Catalog)
how tables/views/functions/types, etc. are represented

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<< Cost ModelsThroughout this course, we compare costs of DB operationsImportant aspects in determining cost: data is always transferred to/from disk as whole blocks (pages) cost of manipulating tuples in memory is negligible overall cost determined primarily by #data-blocks read/writtenComplicating factors in determining costs: not all page accesses require disk access (buffer pool) tuples typically have variable size (tuples/page ?)More details later …COMP9315 21T1 Storage Management [10/10]Produced: 17 Feb 2021