prologic
twtxt.net
 (2w ago)
↳ In-reply-to » Problem 2: Your SSD-backed database has a usage-pattern that rewards you with a 80% page-cache hit-rate (i.e. 80% of disk reads are served directly out of memory instead of going to the SSD). The median is 50 distinct disk pages for a query to gather its query results (e.g. InnoDB pages in MySQL). What is the expected average query time from your database?

  • Page size 1MB
  • Median 50 pages per query
  • 80% pages cached
  • 200us SSD reads
  • 100us Memory reads
  • Query time:
    • (50x0.80x100)+(50x0.20x200)โ€Žโ€‰=โ€‰6,000
    • 6000us
    • 6ms

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