Skip to content

Latest commit

 

History

History
65 lines (54 loc) · 2.37 KB

storage_management.md

File metadata and controls

65 lines (54 loc) · 2.37 KB
Raw

Storage Management

Low Level View

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.

Comparison of Storage Devices

RAM HDD SDD
Read latency ~1 micro ~10 milli ~50 micro
Write latency ~1 micro ~10 milli ~900 micro
Read unit byte block (e.g. 1 KB) byte
Writing byte write a block write on empty block

Aim of DBMS

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 minimize disk/memory transfers.
  • Interpret loaded data as tuples/records.
  • Basis for file structures used by access methods.

Views of Data in Query Evaluation

Representing Database Objects During Query Execution

  • DB (handle on an authorized/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.

Topics In Storage Management

  • Disks and files.
    • Performance issues and organization 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.

Cost Models

Important aspects in determining costs of DB operations:

  • 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/written.

Complicating factors in determining costs:

  • Not all page accesses require disk access (buffer pool).
  • Tuples typically have variable size (tuples/page?).