Google Spanner: our understanding of concepts and implications Harisankar H DOS lab weekly seminar 8/Dec/2012 http://harisankarh.wordpress.com "Google Spanner: our understanding of concepts and implications" by Harisankar H is licensed under a Creative Commons Attribution 3.0 Unported License .
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Google Spanner : our understanding of concepts and implications
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Google Spanner: our understanding of concepts and implications
Harisankar HDOS lab weekly seminar
8/Dec/2012http://harisankarh.wordpress.com
"Google Spanner: our understanding of concepts and implications" by Harisankar H is licensed under a Creative Commons Attribution 3.0 Unported License.
Jerry unfriends Tom to write a controversial comment
T1: Jerry unfriends TomT2: Jerry posts comment T3: Tom views Jerry’s profile
If serial order is as above, Jerry will be in trouble!
Formally, “If commit of T1 preceded the initiation of a new transaction T2 in wall-clock(physical) time, then commit of T1 should precede commit of T2 in the serial ordering also. ”
• Snapshot isolation– Transactions read a consistent snapshot of the database– Values written should not have conflicting updates after the
snapshot was read– E.g., R1(X)R1(Y) R2(X)R2(Y) W2(Y) W1(X) is allowed– Weaker than serializability, but more efficient(lock-free)– Spanner do not allow writes for these transactions
» Probably, that is how they preserve isolation
– Snapshot read• Read of a consistent state of the database in the past
Hierarchical data model
– Universes(Spanner deployment)• Databases(collection of tables)
– Tables with schemas
» Ordered Rows, columns
» One or more primary-key columns
• Rows named during primary keys
– Hierarchies of tables
» Directory tables(top of table hierarchy)
• Directories
• Each row in directory table(with key K) along with the rows in descendant tables that start with K form a directory
Fig: a
Figures (a),(b) from Spanner, OSDI 2012 paper
User perspective: database configuration
• Database placement and reliability– Administrator:
• Create options which specify number of replicas and placement