Databases Reference
In-Depth Information
Virtual Address Space
Every Windows process has its own virtual address space (VAS), the size of which varies according
to processor architecture (32-bit or 64-bit) and the operating system edition. The VAS is a i xed-size
resource that can be exhausted (even on 64-bit computers) while physical memory is still available.
Memory Performance Counters
Table 10-4 outlines the PerfMon counters that are key to gathering information about memory
availability and consumption.
TABLE 10-4:
Key Memory PerfMon Counters
COUNTER
WHAT TO LOOK FOR
PROBLEM
CONDITION
Memory
Available
Mbytes
Amount of free physical memory in MB; values below
100MB could indicate external memory pressure or a
max server memory setting that's too high.
<100MB
Memory
Pages/sec
A high value doesn't necessarily mean a problem;
review this counter if you suspect external memory
pressure and always consider in the context of other
memory counters.
<500
Memory
Free System
Page Table
Entries
Page Table Entries are most likely to become depleted
(and therefore a bottleneck) on x86 servers, particularly
where /3GB or /USERVA switches are used.
<5000
Paging File
% Usage,
% Usage Peak
Generally, workload increases the demand for virtual
address pace (VAS), which increases the demand for
Page File. Heavy reliance on page fi le use is usually
an indication of memory problems. The threshold will
depend on the size of your pagefi le. See Chapter 3 for
sizing details.
>70%
MSSQL
Buf er
Manager
Page Life
Expectancy
Duration, in seconds, that a data page resides in the buf-
fer pool. A server with sui cient memory has high page
life expectancy. Watch the trend of this counter over time.
Overall it should stay stable or trend higher. Frequent
dips of the value can indicate memory pressure.
<300
seconds
MSSQL
Buf er
Manager
Buf er Cache
Hit Ratio
Percent of page requests satisfi ed by data pages from
the buf er pool. Page Life Expectancy is a better overall
indicator of buf er pool health.
<98%
MSSQL
Buf er
Manager
Lazy Writes/
sec
Number of times per second SQL Server relocates dirty
pages from buf er pool (memory) to disk
>20
Search WWH ::
Custom Search