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Virtualized Databases?
Virtualization is an old concept that provides abstraction and security through CPU execution modes and virtual memory management. There are two main challenges for virtualization - handling privileges and virtual memory address translation. Hardware virtualization techniques address these by introducing a hypervisor mode and advanced page table structures, improving performance over older binary translation methods. Database performance in virtualized environments is impacted by the overhead of interrupts, system calls, and memory management, so optimization techniques focus on reducing these costs through configuration tuning, hardware choices, and I/O isolation strategies.
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Virtualized Databases?
- 1. VIRTUALIZED DATABASES? Approach: mechanicsof virtualization "certain big players" will not be mentioned Talk is general, mostly about hardware issues which are the same for any platform
- 2. ME • Liz van Dijk (@lizztheblizz) • Working at Sizing Servers Research Lab • First-timer at FOSDEM! • Not really a developer, not really a sysadmin, not really a DBA •I just like knowing how stuff works.
- 3. SO... VIRTUALIZATION, HUH. • It’s far too broad a term • It’s a pretty old concept. (about half a century, actually) • Its main purposes are abstraction and security • Making use of the correct CPU execution mode • Managing Virtual Memory History! Broad term, 100 different meanings Full-system virtualization on the mainframes in the 60's IBM m44, trap and emulate Recently: * x86 did not support full virtualization, trap and emulate did not work * multicore hardware, single threaded software. Inefficient datacenters. Full Virtualization is not the only virtualization combination of different methods Who uses RAID? Who uses Virtual Memory? 2 big issues that all solutions try to work around Focus on these, the next steps should be more or less logical Problem 1: matter of privileges kernels assume full control over hardware how does the hardware deal with this? layer-based security system (onion) 2-bit code in memory address, cpu verifies the code, does or doesn't do the instruction x86: 4 layers code 00: supervisor mode code 11: user mode
- 4. SO... VIRTUALIZATION, HUH. • It’s far too broad a term • It’s a pretty old concept. (about half a century, actually) • Its main purposes are abstraction and security • Making use of the correct CPU execution mode • Managing Virtual Memory History! Broad term, 100 different meanings Full-system virtualization on the mainframes in the 60's IBM m44, trap and emulate Recently: * x86 did not support full virtualization, trap and emulate did not work * multicore hardware, single threaded software. Inefficient datacenters. Full Virtualization is not the only virtualization combination of different methods Who uses RAID? Who uses Virtual Memory? 2 big issues that all solutions try to work around Focus on these, the next steps should be more or less logical Problem 1: matter of privileges kernels assume full control over hardware how does the hardware deal with this? layer-based security system (onion) 2-bit code in memory address, cpu verifies the code, does or doesn't do the instruction x86: 4 layers code 00: supervisor mode code 11: user mode
- 5. SO... VIRTUALIZATION, HUH. • It’s far too broad a term • It’s a pretty old concept. (about half a century, actually) • Its main purposes are abstraction and security • Making use of the correct CPU execution mode • Managing Virtual Memory History! Broad term, 100 different meanings Full-system virtualization on the mainframes in the 60's IBM m44, trap and emulate Recently: * x86 did not support full virtualization, trap and emulate did not work * multicore hardware, single threaded software. Inefficient datacenters. Full Virtualization is not the only virtualization combination of different methods Who uses RAID? Who uses Virtual Memory? 2 big issues that all solutions try to work around Focus on these, the next steps should be more or less logical Problem 1: matter of privileges kernels assume full control over hardware how does the hardware deal with this? layer-based security system (onion) 2-bit code in memory address, cpu verifies the code, does or doesn't do the instruction x86: 4 layers code 00: supervisor mode code 11: user mode
- 6. X86 VIRTUALIZATION • Binary Translation, aka “faking it” • Applies ring deprivileging, and translates “bad calls” on the fly • “Full” Hardware Virtualization • Introduced Ring -1: Hypervisor mode • Only intervenes when absolutely necessary BT, old awesome, employed by QEMU and wine. Less relevant now for full-virtualization ring deprivileging, look it up! Intel/AMD caught up, implemented VT-x and AMD-V ring -1: hypervisor Let OS'es do whatever they want, but use trap and emulate extra roundtrip, extra overhead CPU has more tasks to perform, but they also take longer newer cpu is better
- 7. X86 VIRTUALIZATION • Binary Translation, aka “faking it” • Applies ring deprivileging, and translates “bad calls” on the fly • “Full” Hardware Virtualization • Introduced Ring -1: Hypervisor mode • Only intervenes when absolutely necessary BT, old awesome, employed by QEMU and wine. Less relevant now for full-virtualization ring deprivileging, look it up! Intel/AMD caught up, implemented VT-x and AMD-V ring -1: hypervisor Let OS'es do whatever they want, but use trap and emulate extra roundtrip, extra overhead CPU has more tasks to perform, but they also take longer newer cpu is better
- 8. X86 VIRTUALIZATION • Binary Translation, aka “faking it” • Applies ring deprivileging, and translates “bad calls” on the fly • “Full” Hardware Virtualization • Introduced Ring -1: Hypervisor mode • Only intervenes when absolutely necessary BT, old awesome, employed by QEMU and wine. Less relevant now for full-virtualization ring deprivileging, look it up! Intel/AMD caught up, implemented VT-x and AMD-V ring -1: hypervisor Let OS'es do whatever they want, but use trap and emulate extra roundtrip, extra overhead CPU has more tasks to perform, but they also take longer newer cpu is better
- 9. VIRTUAL MEMORY 0xA 0xB 0xC 0xD 0xE 0xF 0xG 0xH CPU Mem Managed by software Actual Hardware Problem 2: Virtual memory 4kb physical segments with physical addresses software: pages very easy to manage in OS, all software gets a continuous block page table keeps track of physical to virtual mapping TLB cache keeps track of these mappings, very fast needs to flush every context switch.
- 10. VIRTUAL MEMORY Virtual 0xA Memory 0xB 1 0xC 2 0xD 3 0xE 4 0xF 5 0xG OS 6 7 0xH CPU 8 9 Mem 10 11 12 Managed by software Actual Hardware Problem 2: Virtual memory 4kb physical segments with physical addresses software: pages very easy to manage in OS, all software gets a continuous block page table keeps track of physical to virtual mapping TLB cache keeps track of these mappings, very fast needs to flush every context switch.
- 11. VIRTUAL MEMORY Virtual Page Table 0xA Memory 0xB 1 1 | 0xD 0xC 2 2 | 0xC 0xD 3 3 | 0xF 0xE 4 4 | 0xA 0xF 5 5 | 0xH 0xG OS 6 7 6 | 0xG 7 | 0xB 0xH CPU 8 9 8 | 0xE Mem 10 11 etc. 12 Managed by software Actual Hardware Problem 2: Virtual memory 4kb physical segments with physical addresses software: pages very easy to manage in OS, all software gets a continuous block page table keeps track of physical to virtual mapping TLB cache keeps track of these mappings, very fast needs to flush every context switch.
- 12. VIRTUAL MEMORY Virtual Page Table 0xA Memory 0xB 1 1 | 0xD 0xC 2 2 | 0xC 0xD TLB 3 3 | 0xF 0xE 1 | 0xD 4 4 | 0xA 0xF 5 | 0xH 5 5 | 0xH 0xG 2 | 0xC OS 6 7 6 | 0xG 7 | 0xB 0xH CPU 8 9 8 | 0xE Mem etc. 10 11 etc. 12 Managed by software Actual Hardware Problem 2: Virtual memory 4kb physical segments with physical addresses software: pages very easy to manage in OS, all software gets a continuous block page table keeps track of physical to virtual mapping TLB cache keeps track of these mappings, very fast needs to flush every context switch.
- 13. SPT VS HAP “Read-only” 0xA Page Table 0xB 1 | 0xD 0xC 1 2 5 | 0xH 0xD VM A 3 2 | 0xC 0xE 0xF 4 5 0xG N 0xH CPU 1 12 | 0xB 10 | 0xE Mem 2 VM B 3 9 | 0xA 4 12 etc. Managed by VM OS Managed by hypervisor Actual Hardware 2 methods locked page table, access generates trap, VMM handles memory access much slower memory access EPT/RVI/HAP Make TLB much bigger, make it smarter, VM-aware much more complex to fill up, though. slow initial memory access filled TLB is very fast, tho.
- 14. SPT VS HAP “Read-only” “Shadow” 0xA Page Table Page Table 0xB 1 | 0xD 1 | 0xG 0xC 1 5 | 0xH 5 | 0xD 0xD 2 VM A 3 2 | 0xC 2 | 0xF 0xE 0xF 4 5 N A 0xG 0xH CPU 1 12 | 0xB 10 | 0xE 12 | 0xE 10 | 0xB Mem 2 VM B 3 9 | 0xA 9 | 0xC 4 12 etc. B Managed by VM OS Managed by hypervisor Actual Hardware 2 methods locked page table, access generates trap, VMM handles memory access much slower memory access EPT/RVI/HAP Make TLB much bigger, make it smarter, VM-aware much more complex to fill up, though. slow initial memory access filled TLB is very fast, tho.
- 15. SPT VS HAP “Read-only” 0xA Page Table TLB 0xB 1 | 0xD 0xC A1 | 0xD 1 5 | 0xH 0xD A5 | 0xH 2 VM A 3 2 | 0xC 0xE 0xF A2 | 0xC B12 | 0xB 4 5 0xG B10 | 0xE N 0xH B9 | 0xA CPU 1 12 | 0xB 10 | 0xE Mem 2 VM B 3 9 | 0xA 4 12 etc. etc. Managed by VM OS Managed by hypervisor Actual Hardware 2 methods locked page table, access generates trap, VMM handles memory access much slower memory access EPT/RVI/HAP Make TLB much bigger, make it smarter, VM-aware much more complex to fill up, though. slow initial memory access filled TLB is very fast, tho.
- 16. WHAT DOES THISTEACH US? • All “kernel” activity is a lot more costly: • Interrupts • System Calls (I/O) • Memory page management so, 3 actions are slower in virtualization Interrupts - hardware asking for attention System Calls - software asking for kernel attention Page Management - memory access
- 17. IN THE WILD... •From best to worst case scenario... • Bare-metal (Xen, KVM, ESX, Hyper-V) • Host-based (VirtualBox, VMware Workstation, etc.) • Cloud-based (Amazon, Terremark, etc.)
- 18. BARE-METAL OPTIONS • Know your my.cnf inside out • Use hardware-assisted paging + Large Pages! (InnoDB: large- pages) • Make use of paravirtualized HW options • Take care of all your caching levels • Use DirectIO (innodb_flush_method=O_DIRECT) smalls mistakes in a native environment get bigger in virtual one memory allocations are expensive optimize your my.cnf!!! tools.percona.com good starting point connection-specific buffers (join-buffer, sort-buffer, etc) sweet spot = test!! SWAPPING = EVIL swappiness Large Pages DirectIO
- 19. BARE-METAL OPTIONS • Know your my.cnf inside out • Use hardware-assisted paging + Large Pages! (InnoDB: large- pages) • Make use of paravirtualized HW options • Take care of all your caching levels • Use DirectIO (innodb_flush_method=O_DIRECT) smalls mistakes in a native environment get bigger in virtual one memory allocations are expensive optimize your my.cnf!!! tools.percona.com good starting point connection-specific buffers (join-buffer, sort-buffer, etc) sweet spot = test!! SWAPPING = EVIL swappiness Large Pages DirectIO
- 20. BARE-METAL OPTIONS • Know your my.cnf inside out • Use hardware-assisted paging + Large Pages! (InnoDB: large- pages) • Make use of paravirtualized HW options • Take care of all your caching levels • Use DirectIO (innodb_flush_method=O_DIRECT) smalls mistakes in a native environment get bigger in virtual one memory allocations are expensive optimize your my.cnf!!! tools.percona.com good starting point connection-specific buffers (join-buffer, sort-buffer, etc) sweet spot = test!! SWAPPING = EVIL swappiness Large Pages DirectIO
- 21. HARDWARE CHOICES •Choosing the right CPU’s • Intel5500/7500 and later types (Nehalem) / All AMD quadcore Opterons (HW-assisted/MMU virtualization) • Choosing the right NIC’s (VMDQ) • Choosing the right storage system (iSCSI vs FC SAN) CPU's listed here support both HW-assist and HAP virtual machine device queueing
- 22. HOST-BASED • All of the above, if possible :) • IO becomes the bigger issue on standard client hardware • Focus on moving database IO away from the same disk you run the host- and guest-OS on. • Consider installing an SSD :) Keep in mind all of the previous things IO is a bigger issue 2 OS'es + DB running on the same disk always a problem separate disk, maybe iSCSI lun? buy an SSD!
- 23. CLOUD-BASED •No control whatsoever over host-system :( • Sometimes unreliable IO • Change strategy! Design for easy sharding and replication! • Caching caching caching! • Consider RDS to reduce operational overhead? Can't escape the hurt unreliable disk IO CACHING sharding/replication to spread write/read load very write-heavy may be more trouble than it's worth asynchronous writes? not very durable Use RDS to cut back operational cost
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