1 / 8

CS 2606 Project 2 Clarifications

CS 2606 Project 2 Clarifications. Clarifications. Output specs Write-through versus write-back buffers The remove operation and the buffer pool Note: all of these clarifications are consistent with the project specs and the sample files posted. Output specs. insert command

mei
Download Presentation

CS 2606 Project 2 Clarifications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CS 2606 Project 2 Clarifications

  2. Clarifications • Output specs • Write-through versus write-back buffers • The remove operation and the buffer pool Note: all of these clarifications are consistent with the project specs and the sample files posted

  3. Output specs • insert command insert #: record length = # + # = #, stored at position # • print command print # <record contents> • remove command remove #: at position #, record length = # Note: if the insert command involves a remove, only the insert operation produces output

  4. Output specs • buffers command buffers: b1 b2 b3 … • freelist command freelist: p1 s1, p2 s2, p3 s3, … Notes: • buffer indices and free list positions begin at 0 • buffer list starts with LRU block, ends with MRU block • free list is sorted by position

  5. Write-through vs Write-back buffers • Write-through buffers: • insert command always results in a physical disk write • Write-back buffers: • physical disk write occurs only when necessary during a page fault (disk writes are minimized) • Write-through buffers are easier to implement, you get extra-credit (5%) if you implement a write-back buffer • In both cases, the insert command affects the buffer pool (blocks involved in the operation become the most recently used blocks)

  6. Example • Suppose size of buffer pool = 2, and all records are 200 bytes each • Consider the sequence: command write-through write-back insert 1 write fblock 1 insert 2 write fblock 1 insert 3 write fblocks 1,2 print 1 print 2 print 3 insert 4 write fblock 2 insert 5 write fblock 2 insert 6 write fblocks 2,3 write fblock 1 no diskoperations

  7. Example, continued • After the last command, buffer pool contains fblocks 2, 3 • If we continue with the following operations: command write-through write-back … insert 6 write fblocks 2,3 write fblock 1 print 1 fblk 1 in, fblk 2 out fblk 1 in, write fblk 2 print 2 print 3 fblk 2 in, fblk 3 out fblk 2 in, write fblk 3 print 4 print 5 print 6 fblk 3 in, fblk 1 out fblk 3 in, no write * * write not necessary because block 1 not dirty

  8. The remove operation • Question: does the remove operation require a buffer pool update or a disk operation? • Maybe, depending on how complex we want this project to be • For simplicity, you may assume that remove is strictly a memory manager operation (refer to the previous slide set about this project); no buffer pool update will result from a remove • Important: you need to deal with obtaining the size of the removed record (keep a table, or retrieve the 4 bytes from the file, without using the buffer pool)

More Related