Transaction Timestamping in Temporal Databases

German Shegalov Transaction Timestamping in Temporal Databases FR Informatik Graduiertenkolleg Ringvorlesung, May 26 th , 2003 based on the research by D. Lomet , C. Jensen and R. Snodgrass

Outline ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Conventional vs. Temporal DB ,[object Object],[object Object],[object Object],[object Object],[object Object]

Notions of Time ,[object Object],[object Object],[object Object],[object Object],[object Object]

Transaction (ACID contract) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Transaction Isolation x=0 r 1 (x=0) r 2 (x=0) w 2 (x=x+20) w 1 (x=x+10) x=30 x=10 Lost Update: w 1 (x=10) r 2 (x=10) abort 1 =w 1 -1 (x) w 2 (x=x+10) x=0 x=10 x=20 Dirty Read: x=0 y=0 x=0 y=10 Inconsistent Read: r 1 (x=0) w 2 (x=5) w 2 (y=10) r 1 (y=10) Read/Write, Write/Read, Write/Write are not commutable

CC Protocols ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

TT Database Semantics ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Timestamp Selection (simple) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Two Phase Commit (2PC) Coordinator DB 1 DB 2 force-log begin Timeline force-log prepared force-log prepared force-log commit force-log commit force-log commit force-log end prepare prepare yes yes commit commit ack ack

Timestamping Issues in 2PC ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

2PC for Transaction Time DB Coordinator DB 1 DB 2 force-log begin(10) Timeline force-log prepared;EARLIEST 1 ++ force-log prepared;EARLIEST 2 ++ force-log commit(11) force-log commit(11) force-log commit(11) force-log end /*begin_time = 10*/ /*EARLIEST 1 = 8*/ /*EARLIEST 2 = 10*/ prepare prepare yes(9) yes(11) commit(11) commit(11) ack ack

Timestamping since SQL-92 ,[object Object],[object Object],[object Object],[object Object]

" Current Time " Matters ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],r(y 0 ) X 1 X 3 time fix t current ct 1 ct 3 w 3 ( y 3 ) X 2 ct 2 w 2 ( y 2 ) buy

Inconsistent Timeslice ,[object Object],[object Object],[object Object],[object Object],time X 1 X 2 x=0 y=0 z=0 5 c 2 fix t 1 current 1 fix t 2 current 3 w 1 (x=1) 2 w 2 ( y=1 ) 4 r 1 (y=1) 6 w 1 (z=2) 7 8 c 1

Unrepeatable Timeslice ,[object Object],X 1 X 2 y=0 y=0 y=1 time X 3 6 c 2 4 c 1 fix t 1 current 2 timeslice 1 (t 1 current ) 3 w 2 ( y=1 ) 5 timeslice 3 ( t 1 current ) 7 8 c 3 fix t 2 current 1

Solution Requirements ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Algorithm Design ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Before t X Assignment ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Timestamp t X Assignment ,[object Object],[object Object],[object Object],[object Object]

"Who comes too late … " ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Optimization I (Precision) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Optimization II ( RTT ) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Commit Processing ,[object Object],[object Object]

System Crashes ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Summary ,[object Object],[object Object],[object Object],[object Object],[object Object]

Outlook ,[object Object],[object Object]

Transaction Timestamping in Temporal Databases

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Transaction Timestamping in Temporal Databases