class 20 updates 2.0 prof. Stratos Idreos

Transcription

1 class 20 updates 2.0 prof. Stratos Idreos

2 UPDATE table_name SET column1=value1,column2=value2,... WHERE some_column=some_value INSERT INTO table_name VALUES (value1,value2,value3,...) updates Stratos Idreos 2 /34

3 the world has changed a little bit by now updates Stratos Idreos 3 /34

4 monitor CPU utilization monitor memory hierarchy utilization monitor clicks (frequency, locations, specific links, sequences) Stratos Idreos 4 /34

5 insert new entry (a,b,c,d, ) on table x update N columns, K trees, statistics, table x A B C D A D B Stratos Idreos 5 /34

6 updates reads A B C D A B C D periodic merge and/or on-the-fly merge write optimized-store read optimized-store A case for fractured mirrors Ravishankar Ramamurthy, David J. DeWitt, Qi Su Very Large Databases Journal (VLDBJ), 2003 Stratos Idreos 6 /34

7 L1 L2 Stratos Idreos 7 /34

8 buffer L1 L2 any problems Stratos Idreos 8 /34

9 L1 L2 Stratos Idreos 9 /34

10 c0 c1 c3 L1 L2 c4 c5 c6 Stratos Idreos 10/34

11 in-place updates: the cardinal sin A(t1) A(t2) A(t3) The Transaction Concept: Virtues and Limitations Jim Gray, Tandem TR 81.3, 1981 Stratos Idreos 11/34

12 what can go wrong? failures & >1 queries Stratos Idreos 12/34

13 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) Stratos Idreos 13/34

14 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) A B C D search (scan/index) to find row to update select+project actions Stratos Idreos 13/34

15 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) A B C D search (scan/index) to find row to update select+project actions A B C D list of rowids (positions) (sort) Stratos Idreos 13/34

16 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) A B C D search (scan/index) to find row to update select+project actions A B C D list of rowids (positions) (sort) we know what to update but nothing happened yet Stratos Idreos 13/34

17 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 level 2 A B C D read page in L1 update persist to L2 if problem (power/abort) before we write all pages we are left with an inconsistent state WAL: keep persistent notes as we go so we can resume or undo Stratos Idreos 14/34

18 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 level 2 A B C D Stratos Idreos 15/34

19 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 level 2 A B C D Stratos Idreos 15/34

20 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 level 2 A B C D Stratos Idreos 15/34

21 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 apply all updates for this page level 2 A B C D Stratos Idreos 15/34

22 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 apply all updates for this page level 2 A B C D N updates in persistent storage Stratos Idreos 15/34

23 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 apply all updates for this page level 2 A B C D N updates in persistent storage (update in place/out of place) problems when failure Stratos Idreos 15/34

24 recovery classic example joe owes mike 100$ both joe and mike have a Bank of Bla account possible actions joe -100 mike mike joe what if there is a failure here? Stratos Idreos 16/34

25 recovery classic example joe owes mike 100$ both joe and mike have a Bank of Bla account possible actions actually 1)read mike; 2) mike+100; 3) write new mike; joe -100 mike mike joe what if there is a failure here? Stratos Idreos 16/34

26 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) CPU level 1 read page in L1 update persist to L2 level 2 A B C D what do we need to remember (log) Stratos Idreos 17/34

27 update all rows where A=v1 & B=v2 to (a=a/2,b=b/4,c=c-3,d=d+2) A B C D search (scan/index) to find row to update select+project actions A B C D list of rowids (positions) (sort) restart: get set of positions again, and either resume from last written page or undo all previously written pages Stratos Idreos 18/34

28 buffer updates memory log buffer updates memory log buffer updates memory log disk SSD non volatile memory disk SSD disk Stratos Idreos 19/34

29 flash disks read/write asymmetry need to erase a block to write it finite number of erase cycles MaSM: efficient online updates in data warehouses Manos Athanassoulis, Shimin Chen, Anastasia Ailamaki, Phillip Gibbons, Radu Stoica ACM SIGMOD Conference, 2011 Stratos Idreos 20/34

30 C Mohan, IBM Research ACM SIGMOD Edgar F. Codd Innovations award 1993 (rumor has it he has his own Facebook server) (also check his nosql lecture) ARIES: A Transaction Recovery Method Supporting Fine-Granularity Locking and Partial Rollbacks Using Write-Ahead Logging C. Mohan, Donald J. Haderle, Bruce G. Lindsay, Hamid Pirahesh, Peter M. Schwarz ACM Transactions on Database Systems, 1992 Stratos Idreos 21/34

31 Χ classic example joe owes mike 100$ both joe and mike have a Bank of Bla account recovery what about logging and recovery during e-shopping e.g., shopping cart, wish list, check out Quantifying eventual consistency with PBS Peter Bailis, Shivaram Venkataraman, Michael J. Franklin, Joseph M. Hellerstein, Ion Stoica Communications of the ACM, 2014 Stratos Idreos 22/34

32 db complex legacy tuning expensive nosql simple clean just enough why nosql as apps become more complex as apps need to be more scalable newsql Mesa: Geo-Replicated, Near Real-Time, Scalable Data Warehousing Ashish Gupta et al. International Conference on Very Large Databases (VLDB), 2014 F1: A Distributed SQL Database That Scales Jeff Shute et al. International Conference on Very Large Databases (VLDB), 2013 (more in 265) Stratos Idreos 23/34

33 all or nothing remember what we changed so we can undo or resume (depends on applications semantics) Stratos Idreos 24/34

34 transaction any database query that can/should be seen as a single task parse optimize plan( read X write Z ) Stratos Idreos 25/34

35 Atomicity Consistency Isolation Durability Jim Gray, IBM, Tandem, DEC, Microsoft ACM Turing award ACM SIGMOD Edgar F. Codd Innovations award Stratos Idreos 26/34

36 all or nothing Atomicity Consistency Isolation Durability correct >1 queries persistent Stratos Idreos 27/34

37 A B C D queries arrive concurrently q1) select A>v1, B=B+b, C=C-c q2) select B>v2, avg(c) q3) select C<v3 & B>v4, A=C q4) write more queries Goal: process queries in parallel leave db in a consistent state return correct results Stratos Idreos 28/34

38 query 1 parse optimize plan( read X write Z ) query 2 parse optimize plan( read Z write Z ) Stratos Idreos 29/34

39 locks wait until lock is free read X get_rlock(x) read X release_rlock(x) R W R yes no W no no write X get_wlock(x) write X release_wlock(x) commit Stratos Idreos 30/34

40 2 phase locking 1. get all locks 2. do all tasks 3. commit 4. release all locks (and variations) HT be positive! - optimistic concurrency control Stratos Idreos 31/34

41 database table1 lock granularity table2 C1 C2 A survey of B-tree logging and recovery techniques Goetz Graefe ACM Trans. Database Systems, 2012 Stratos Idreos 32/34

42 textbook: chapters 16, 17, 18 Stratos Idreos 33/34

43 class 20 updates 2.0 DATA SYSTEMS prof. Stratos Idreos