availability, recovery semantics, and guarantees Vasiliki Kalavri | Boston University 2020 Today’s topics • High-availability and fault-tolerance in distributed stream processing • Recovery semantics and guarantees against failures and guarantee correct results after recovery? • how can we ensure minimal downtime and fast recovery? • how can we hide recovery side-effects from downstream applications? Vasiliki failures. 7 Vasiliki Kalavri | Boston University 2020 Recovery types 8 Vasiliki Kalavri | Boston University 2020 Recovery types • Precise recovery (exactly-once) • It hides the effects of a failure

VMware Data Recovery 管理员指南 ZH_CN-000193-00 VMware Data Recovery 2 VMware, Inc. 您可以在 VMware 的网站上找到最新的技术文档，网址为 http://www.vmware.com/cn/support/ VMware 网站还提供了最新的产品更新。 如果您对本文档有任何意见和建议，请将您的反馈提交到： 1 了解 VMware Data Recovery 7 备份虚拟机 7 卷影复制服务 8 删除重复存储的优点 8 2 安装 VMware Data Recovery 9 VMware Data Recovery 系统要求 9 安装客户端插件 9 安装备份设备 10 向备份设备中添加硬盘 10 3 配置 VMware Data Recovery 13 启动备份设备 13 配置备份设备 VMware Data Recovery 故障排除 18 索引 21 VMware, Inc. 3 VMware Data Recovery 4 VMware, Inc. 关于本文档 《VMware Data Recovery 管理员指南》包含为中小型企业建立备份解决方案的信息。 目标读者 本文档适用于需要使用 VMware Data Recovery 提供备份解决方案的用户。本书的目标读者为熟悉虚拟机技术

K1: Data Stream Processing and Analytics Spring 2020 2/04: Streaming languages and operator semantics Vasiliki Kalavri | Boston University 2020 Vasiliki Kalavri | Boston University 2020 Languages Almost universally supported across streaming systems and languages albeit with various names and semantics • Allow un-blocking the processing of blocking operators by defining bounded portions of the Continuous queries on data streams • New streams (derived) are defined as virtual views in SQL • Semantics are equivalent to having an append-only table to which new tuples are continuously added. 34

missing, out-of-order, delayed data 4. Guarantee deterministic (on replay) and correct results (on recovery) 5. Combine batch (historical) and stream processing 6. Ensure availability despite failures streams that describe the changing view computed over the input stream according to the relational semantics of the operator. 19 Vasiliki Kalavri | Boston University 2020 • Base streams update relation streams that describe the changing view computed over the input stream according to the relational semantics of the operator. src dest bytes 1 2 20K 2 5 32K src dest total 1 2 20K 2 5 32K sum Results

alternatives • Runtime optimizations • load management, scheduling, state management • Optimization semantics, correctness, profitability Topics covered in this lecture ??? Vasiliki Kalavri | Boston University basics 4 Dataflow graph • operators are nodes, data channels are edges • channels have FIFO semantics • streams of data elements flow continuously along edges Operators • receive one or more conditions does the optimization preserve correctness? • maintain state semantics • maintain result and selectivity semantics • Dynamism: can the optimization be applied during runtime or does it

bindings, a com- mon layer provides the method VirtualBoxManager.waitForEvents(ms) with similar semantics. Things get somewhat more complicated for situations where an application using VirtualBox cannot time outs, or this event is processed. Event must be waitable for this operation to have described semantics, for non-waitable returns true immediately. 62 IEventListener Event listener. An event listener window, or zero if this method has performed all actions necessary to implement the show window semantics for the given platform and/or this VirtualBox front-end. 192 ISnapshot The ISnapshot interface

bindings, a com- mon layer provides the method VirtualBoxManager.waitForEvents(ms) with similar semantics. Things get somewhat more complicated for situations where an application using VirtualBox cannot time outs, or this event is processed. Event must be waitable for this operation to have described semantics, for non-waitable returns true immediately. 5.51 IEventListener Event listener. An event listener window, or zero if this method has performed all actions necessary to implement the show window semantics for the given platform and/or this VirtualBox front-end. 5.182 ISnapshot The ISnapshot interface

bindings, a com- mon layer provides the method VirtualBoxManager.waitForEvents(ms) with similar semantics. Things get somewhat more complicated for situations where an application using VirtualBox cannot time outs, or this event is processed. Event must be waitable for this operation to have described semantics, for non-waitable returns true immediately. 5.51 IEventListener Event listener. An event listener window, or zero if this method has performed all actions necessary to implement the show window semantics for the given platform and/or this VirtualBox front-end. 5.179 ISnapshot The ISnapshot interface

bindings, a com- mon layer provides the method VirtualBoxManager.waitForEvents(ms) with similar semantics. Things get somewhat more complicated for situations where an application using VirtualBox cannot time outs, or this event is processed. Event must be waitable for this operation to have described semantics, for non-waitable returns true immediately. 62 IEventListener Event listener. An event listener window, or zero if this method has performed all actions necessary to implement the show window semantics for the given platform and/or this VirtualBox front-end. 192 ISnapshot The ISnapshot interface

bindings, a com- mon layer provides the method VirtualBoxManager.waitForEvents(ms) with similar semantics. Things get somewhat more complicated for situations where an application using VirtualBox cannot time outs, or this event is processed. Event must be waitable for this operation to have described semantics, for non-waitable returns true immediately. 6.52 IEventListener Event listener. An event listener window, or zero if this method has performed all actions necessary to implement the show window semantics for the given platform and/or this VirtualBox front-end. 6.198 ISnapshot The ISnapshot interface