Here is the latest version of my Diagnostic Information Queries for SQL Server 2008 and SQL Server 2008 R2. These are very useful for determining the configuration, health, and performance of a SQL Server instance and individual database.

I have added a couple of new queries, and added some more interpretation information (as comments) to the queries. The queries start out at the instance level, and then they switch to the database level (so make sure you are pointing at the database you are concerned with). Most of these queries require VIEW SERVER STATE permission.

-- SQL Server 2008 and R2 Diagnostic Information Queries
-- Glenn Berry
-- September 2010
-- http://glennberrysqlperformance.spaces.live.com/
-- Twitter: GlennAlanBerry

-- Instance level queries *******************************

-- SQL and OS Version information for current instance
SELECT @@VERSION AS [SQL Server and OS Version Info];

-- SQL Server 2008 RTM is considered an "unsupported service pack"
-- as of April 13, 2010
-- SQL Server 2008 RTM Builds     SQL Server 2008 SP1 Builds     SQL Server 2008 SP2 Builds
-- Build       Description        Build        Description         Build     Description
-- 1600        Gold RTM
-- 1763        RTM CU1
-- 1779        RTM CU2
-- 1787        RTM CU3    -->      2531        SP1 RTM
-- 1798        RTM CU4    -->      2710        SP1 CU1
-- 1806        RTM CU5    -->      2714        SP1 CU2
-- 1812        RTM CU6    -->      2723        SP1 CU3
-- 1818        RTM CU7    -->      2734        SP1 CU4
-- 1823        RTM CU8    -->      2746        SP1 CU5
-- 1828        RTM CU9    -->      2757        SP1 CU6
-- 1835        RTM CU10   -->     2766        SP1 CU7
-- RTM Branch Retired     -->     2775        SP1 CU8      -->  3798       SP2 CTP
--                                            2789         SP1 CU9                                  

-- SQL Azure Builds (most DMV queries don't work on SQL Azure)
-- Build            Description
-- 10.25.9200       RTM Service Update 1
-- 10.25.9268       RTM Service Update 2
-- 10.25.9331       RTM Service Update 3
-- 10.25.9386       RTM Service Update 4

-- SQL Server 2008 R2 Builds
-- Build            Description
-- 10.50.1092        August 2009 CTP2
-- 10.50.1352        November 2009 CTP3
-- 10.50.1450        Release Candidate
-- 10.50.1600        RTM
-- 10.50.1702        RTM CU1
-- 10.50.1720        RTM CU2
-- 10.50.1734        RTM CU3

-- Hardware information from SQL Server 2008
-- (Cannot distinguish between HT and multi-core)
SELECT cpu_count AS [Logical CPU Count], hyperthread_ratio AS [Hyperthread Ratio],
cpu_count/hyperthread_ratio AS [Physical CPU Count],
physical_memory_in_bytes/1048576 AS [Physical Memory (MB)], sqlserver_start_time
FROM sys.dm_os_sys_info;

-- Get configuration values for instance
SELECT name, value, value_in_use, [description]
FROM sys.configurations
ORDER BY name ;

-- Focus on
-- backup compression default
-- clr enabled (only enable if it is needed)
-- lightweight pooling (should be zero)
-- max degree of parallelism
-- max server memory (MB) (set to an appropriate value)
-- optimize for ad hoc workloads (should be 1)
-- priority boost (should be zero)

-- File Names and Paths for TempDB and all user databases in instance
SELECT DB_NAME([database_id])AS [Database Name],
       [file_id], name, physical_name, type_desc, state_desc, size
FROM sys.master_files
WHERE [database_id] > 4
AND [database_id] <> 32767
OR [database_id] = 2;

-- Things to look at:
-- Are data files and log files on different drives?
-- Is everything on the C: drive?
-- Is TempDB on dedicated drives?
-- Are there multiple data files?

-- Calculates average stalls per read, per write, and per total input/output for each database file.
SELECT DB_NAME(fs.database_id) AS [Database Name], mf.physical_name, io_stall_read_ms, num_of_reads,
CAST(io_stall_read_ms/(1.0 + num_of_reads) AS NUMERIC(10,1)) AS [avg_read_stall_ms],io_stall_write_ms,
num_of_writes,CAST(io_stall_write_ms/(1.0+num_of_writes) AS NUMERIC(10,1)) AS [avg_write_stall_ms],
io_stall_read_ms + io_stall_write_ms AS [io_stalls], num_of_reads + num_of_writes AS [total_io],
CAST((io_stall_read_ms + io_stall_write_ms)/(1.0 + num_of_reads + num_of_writes) AS NUMERIC(10,1))
AS [avg_io_stall_ms]
FROM sys.dm_io_virtual_file_stats(null,null) AS fs
INNER JOIN sys.master_files AS mf
ON fs.database_id = mf.database_id
AND fs.[file_id] = mf.[file_id]
ORDER BY avg_io_stall_ms DESC;

-- Helps determine which database files on the entire instance have the most I/O bottlenecks

-- Recovery model, log reuse wait description, log file size, log usage size
-- and compatibility level for all databases on instance
SELECT db.[name] AS [Database Name], db.recovery_model_desc AS [Recovery Model],
db.log_reuse_wait_desc AS [Log Reuse Wait Description],
ls.cntr_value AS [Log Size (KB)], lu.cntr_value AS [Log Used (KB)],
CAST(CAST(lu.cntr_value AS FLOAT) / CAST(ls.cntr_value AS FLOAT)AS DECIMAL(18,2)) * 100 AS [Log Used %],
db.[compatibility_level] AS [DB Compatibility Level],
db.page_verify_option_desc AS [Page Verify Option], db.is_auto_update_stats_on,
db.is_auto_update_stats_async_on, db.is_parameterization_forced, db.is_supplemental_logging_enabled,
db.snapshot_isolation_state_desc, db.is_read_committed_snapshot_on
FROM sys.databases AS db
INNER JOIN sys.dm_os_performance_counters AS lu
ON db.name = lu.instance_name
INNER JOIN sys.dm_os_performance_counters AS ls
ON db.name = ls.instance_name
WHERE lu.counter_name LIKE N'Log File(s) Used Size (KB)%'
AND ls.counter_name LIKE N'Log File(s) Size (KB)%'
AND ls.cntr_value > 0;

-- Things to look at:
-- How many databases are on the instance?
-- What recovery models are they using?
-- What is the log reuse wait description?
-- How full are the transaction logs ?
-- What compatibility level are they on?

-- Clear Wait Stats
-- DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR);

-- Isolate top waits for server instance since last restart or statistics clear
WITH Waits AS
(SELECT wait_type, wait_time_ms / 1000. AS wait_time_s,
100. * wait_time_ms / SUM(wait_time_ms) OVER() AS pct,
ROW_NUMBER() OVER(ORDER BY wait_time_ms DESC) AS rn
FROM sys.dm_os_wait_stats
WHERE wait_type NOT IN ('CLR_SEMAPHORE','LAZYWRITER_SLEEP','RESOURCE_QUEUE','SLEEP_TASK'
,'SLEEP_SYSTEMTASK','SQLTRACE_BUFFER_FLUSH','WAITFOR', 'LOGMGR_QUEUE','CHECKPOINT_QUEUE'
,'REQUEST_FOR_DEADLOCK_SEARCH','XE_TIMER_EVENT','BROKER_TO_FLUSH','BROKER_TASK_STOP','CLR_MANUAL_EVENT'
,'CLR_AUTO_EVENT','DISPATCHER_QUEUE_SEMAPHORE', 'FT_IFTS_SCHEDULER_IDLE_WAIT'
,'XE_DISPATCHER_WAIT', 'XE_DISPATCHER_JOIN', 'SQLTRACE_INCREMENTAL_FLUSH_SLEEP'))
SELECT W1.wait_type,
CAST(W1.wait_time_s AS DECIMAL(12, 2)) AS wait_time_s,
CAST(W1.pct AS DECIMAL(12, 2)) AS pct,
CAST(SUM(W2.pct) AS DECIMAL(12, 2)) AS running_pct
FROM Waits AS W1
INNER JOIN Waits AS W2
ON W2.rn <= W1.rn
GROUP BY W1.rn, W1.wait_type, W1.wait_time_s, W1.pct
HAVING SUM(W2.pct) - W1.pct < 99; -- percentage threshold

-- Common Significant Wait types with BOL explanations

-- *** Network Related Waits ***
-- ASYNC_NETWORK_IO        Occurs on network writes when the task is blocked behind the network

-- *** Locking Waits ***
-- LCK_M_IX                Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock
-- LCK_M_IU                Occurs when a task is waiting to acquire an Intent Update (IU) lock
-- LCK_M_S                Occurs when a task is waiting to acquire a Shared lock

-- *** I/O Related Waits ***
-- ASYNC_IO_COMPLETION  Occurs when a task is waiting for I/Os to finish
-- IO_COMPLETION        Occurs while waiting for I/O operations to complete.
--                      This wait type generally represents non-data page I/Os. Data page I/O completion waits appear
--                      as PAGEIOLATCH_* waits
-- PAGEIOLATCH_SH        Occurs when a task is waiting on a latch for a buffer that is in an I/O request.
--                      The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.
-- PAGEIOLATCH_EX        Occurs when a task is waiting on a latch for a buffer that is in an I/O request.
--                      The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.
-- WRITELOG             Occurs while waiting for a log flush to complete.
--                      Common operations that cause log flushes are checkpoints and transaction commits.
-- PAGELATCH_EX            Occurs when a task is waiting on a latch for a buffer that is not in an I/O request.
--                      The latch request is in Exclusive mode.
-- BACKUPIO                Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data

-- *** CPU Related Waits ***
-- SOS_SCHEDULER_YIELD  Occurs when a task voluntarily yields the scheduler for other tasks to execute.
--                      During this wait the task is waiting for its quantum to be renewed.

-- THREADPOOL            Occurs when a task is waiting for a worker to run on.
--                      This can indicate that the maximum worker setting is too low, or that batch executions are taking
--                      unusually long, thus reducing the number of workers available to satisfy other batches.
-- CX_PACKET            Occurs when trying to synchronize the query processor exchange iterator
--                        You may consider lowering the degree of parallelism if contention on this wait type becomes a problem

-- Signal Waits for instance
SELECT CAST(100.0 * SUM(signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2))
AS [%signal (cpu) waits],
CAST(100.0 * SUM(wait_time_ms - signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2))
AS [%resource waits]
FROM sys.dm_os_wait_stats;

-- Signal Waits above 10-15% is usually a sign of CPU pressure

-- Get CPU Utilization History for last 144 minutes (in one minute intervals)
-- This version works with SQL Server 2008 and SQL Server 2008 R2 only
DECLARE @ts_now bigint = (SELECT cpu_ticks/(cpu_ticks/ms_ticks)FROM sys.dm_os_sys_info);

SELECT TOP(144) SQLProcessUtilization AS [SQL Server Process CPU Utilization],
               SystemIdle AS [System Idle Process],
               100 - SystemIdle - SQLProcessUtilization AS [Other Process CPU Utilization],
               DATEADD(ms, -1 * (@ts_now - [timestamp]), GETDATE()) AS [Event Time]
FROM (
      SELECT record.value('(./Record/@id)[1]', 'int') AS record_id,
            record.value('(./Record/SchedulerMonitorEvent/SystemHealth/SystemIdle)[1]', 'int')
            AS [SystemIdle],
            record.value('(./Record/SchedulerMonitorEvent/SystemHealth/ProcessUtilization)[1]',
            'int')
            AS [SQLProcessUtilization], [timestamp]
      FROM (
            SELECT [timestamp], CONVERT(xml, record) AS [record]
            FROM sys.dm_os_ring_buffers
            WHERE ring_buffer_type = N'RING_BUFFER_SCHEDULER_MONITOR'
            AND record LIKE N'%<SystemHealth>%') AS x
      ) AS y
ORDER BY record_id DESC;

-- Good basic information about memory amounts and state
SELECT total_physical_memory_kb, available_physical_memory_kb,
       total_page_file_kb, available_page_file_kb,
       system_memory_state_desc
FROM sys.dm_os_sys_memory;

-- You want to see "Available physical memory is high"

-- SQL Server Process Address space info
--(shows whether locked pages is enabled, among other things)
SELECT physical_memory_in_use_kb,locked_page_allocations_kb,
       page_fault_count, memory_utilization_percentage,
       available_commit_limit_kb, process_physical_memory_low,
       process_virtual_memory_low
FROM sys.dm_os_process_memory;

-- You want to see 0 for process_physical_memory_low
-- You want to see 0 for process_virtual_memory_low

-- Page Life Expectancy (PLE) value for default instance
SELECT cntr_value AS [Page Life Expectancy]
FROM sys.dm_os_performance_counters
WHERE OBJECT_NAME = N'SQLServer:Buffer Manager' -- Modify this if you have named instances
AND counter_name = N'Page life expectancy';

-- PLE is a good measurement of memory pressure.
-- Higher PLE is better. Below 300 is generally bad.
-- Watch the trend, not the absolute value.

-- Buffer cache hit ratio for default instance
SELECT (a.cntr_value * 1.0 / b.cntr_value) * 100.0 AS [Buffer Cache Hit Ratio]
FROM sys.dm_os_performance_counters AS a
INNER JOIN (SELECT cntr_value, [OBJECT_NAME]
            FROM sys.dm_os_performance_counters 
            WHERE counter_name = N'Buffer cache hit ratio base'
            AND [OBJECT_NAME] = N'SQLServer:Buffer Manager') AS b -- Modify this if you have named instances
ON a.[OBJECT_NAME] = b.[OBJECT_NAME]
WHERE a.counter_name = N'Buffer cache hit ratio'
AND a.[OBJECT_NAME] = N'SQLServer:Buffer Manager'; -- Modify this if you have named instances

-- Shows the percentage that SQL Server is finding requested data in memory
-- A higher percentage is better than a lower percentage
-- Watch the trend, not the absolute value.

-- Memory Clerk Usage for instance
-- Look for high value for CACHESTORE_SQLCP (Ad-hoc query plans)
SELECT TOP(20) [type], [name], SUM(single_pages_kb) AS [SPA Mem, Kb]
FROM sys.dm_os_memory_clerks
GROUP BY [type], [name] 
ORDER BY SUM(single_pages_kb) DESC;

-- CACHESTORE_SQLCP  SQL Plans         These are cached SQL statements or batches that aren't in
--                                     stored procedures, functions and triggers
-- CACHESTORE_OBJCP  Object Plans      These are compiled plans for stored procedures,
--                                     functions and triggers
-- CACHESTORE_PHDR   Algebrizer Trees  An algebrizer tree is the parsed SQL text that
--                                     resolves the table and column names

-- Find single-use, ad-hoc queries that are bloating the plan cache
SELECT TOP(100) [text], cp.size_in_bytes
FROM sys.dm_exec_cached_plans AS cp
CROSS APPLY sys.dm_exec_sql_text(plan_handle)
WHERE cp.cacheobjtype = N'Compiled Plan'
AND cp.objtype = N'Adhoc'
AND cp.usecounts = 1
ORDER BY cp.size_in_bytes DESC;

-- Gives you the text and size of single-use ad-hoc queries that waste space in the plan cache
-- Enabling 'optimize for ad hoc workloads' for the instance can help (SQL Server 2008 and 2008 R2 only)
-- Enabling forced parameterization for the database can help, but test first!

-- Database specific queries *****************************************************************

-- **** Switch to a user database *****
USE YourDatabaseName;
GO

-- Individual File Sizes and space available for current database
SELECT name AS [File Name] , physical_name AS [Physical Name], size/128.0 AS [Total Size in MB],
size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS int)/128.0 AS [Available Space In MB], [file_id]
FROM sys.database_files;

-- Look at how large and how full the files are and where they are located
-- Make sure the transaction log is not full!!

-- Top Cached SPs By Execution Count (SQL 2008)
SELECT TOP(25) p.name AS [SP Name], qs.execution_count,
ISNULL(qs.execution_count/DATEDIFF(Second, qs.cached_time, GETDATE()), 0) AS [Calls/Second],
qs.total_worker_time/qs.execution_count AS [AvgWorkerTime], qs.total_worker_time AS [TotalWorkerTime], 
qs.total_elapsed_time, qs.total_elapsed_time/qs.execution_count AS [avg_elapsed_time],
qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY qs.execution_count DESC;

-- Tells you which cached stored procedures are called the most often
-- This helps you characterize and baseline your workload

-- Top Cached SPs By Avg Elapsed Time (SQL 2008)
SELECT TOP(25) p.name AS [SP Name], qs.total_elapsed_time/qs.execution_count AS [avg_elapsed_time],
qs.total_elapsed_time, qs.execution_count, ISNULL(qs.execution_count/DATEDIFF(Second, qs.cached_time,
GETDATE()), 0) AS [Calls/Second], qs.total_worker_time/qs.execution_count AS [AvgWorkerTime],
qs.total_worker_time AS [TotalWorkerTime], qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY avg_elapsed_time DESC;

-- This helps you find long-running cached stored procedures

-- Top Cached SPs By Total Worker time (SQL 2008). Worker time relates to CPU cost
SELECT TOP(25) p.name AS [SP Name], qs.total_worker_time AS [TotalWorkerTime],
qs.total_worker_time/qs.execution_count AS [AvgWorkerTime], qs.execution_count,
ISNULL(qs.execution_count/DATEDIFF(Second, qs.cached_time, GETDATE()), 0) AS [Calls/Second],
qs.total_elapsed_time, qs.total_elapsed_time/qs.execution_count
AS [avg_elapsed_time], qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY qs.total_worker_time DESC;

-- This helps you find the most expensive cached stored procedures from a CPU perspective
-- You should look at this if you see signs of CPU pressure

-- Top Cached SPs By Total Logical Reads (SQL 2008). Logical reads relate to memory pressure
SELECT TOP(25) p.name AS [SP Name], qs.total_logical_reads AS [TotalLogicalReads],
qs.total_logical_reads/qs.execution_count AS [AvgLogicalReads],qs.execution_count,
ISNULL(qs.execution_count/DATEDIFF(Second, qs.cached_time, GETDATE()), 0) AS [Calls/Second],
qs.total_elapsed_time, qs.total_elapsed_time/qs.execution_count
AS [avg_elapsed_time], qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY qs.total_logical_reads DESC;

-- This helps you find the most expensive cached stored procedures from a memory perspective
-- You should look at this if you see signs of memory pressure

-- Top Cached SPs By Total Physical Reads (SQL 2008). Physical reads relate to disk I/O pressure
SELECT TOP(25) p.name AS [SP Name],qs.total_physical_reads AS [TotalPhysicalReads],
qs.total_physical_reads/qs.execution_count AS [AvgPhysicalReads], qs.execution_count,
qs.total_logical_reads,qs.total_elapsed_time, qs.total_elapsed_time/qs.execution_count
AS [avg_elapsed_time], qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY qs.total_physical_reads, qs.total_logical_reads DESC;

-- This helps you find the most expensive cached stored procedures from a read I/O perspective
-- You should look at this if you see signs of I/O pressure or of memory pressure
-- Top Cached SPs By Total Logical Writes (SQL 2008).
-- Logical writes relate to both memory and disk I/O pressure
SELECT TOP(25) p.name AS [SP Name], qs.total_logical_writes AS [TotalLogicalWrites],
qs.total_logical_writes/qs.execution_count AS [AvgLogicalWrites], qs.execution_count,
ISNULL(qs.execution_count/DATEDIFF(Second, qs.cached_time, GETDATE()), 0) AS [Calls/Second],
qs.total_elapsed_time, qs.total_elapsed_time/qs.execution_count AS [avg_elapsed_time],
qs.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats AS qs
ON p.[object_id] = qs.[object_id]
WHERE qs.database_id = DB_ID()
ORDER BY qs.total_logical_writes DESC;

-- This helps you find the most expensive cached stored procedures from a write I/O perspective
-- You should look at this if you see signs of I/O pressure or of memory pressure

-- Lists the top statements by average input/output usage for the current database
SELECT TOP(50) OBJECT_NAME(qt.objectid) AS [SP Name],
(qs.total_logical_reads + qs.total_logical_writes) /qs.execution_count AS [Avg IO],
SUBSTRING(qt.[text],qs.statement_start_offset/2,
    (CASE
        WHEN qs.statement_end_offset = -1
     THEN LEN(CONVERT(nvarchar(max), qt.[text])) * 2
        ELSE qs.statement_end_offset
     END - qs.statement_start_offset)/2) AS [Query Text]   
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt
WHERE qt.[dbid] = DB_ID()
ORDER BY [Avg IO] DESC;

-- Helps you find the most expensive statements for I/O by SP

-- Possible Bad NC Indexes (writes > reads)
SELECT OBJECT_NAME(s.[object_id]) AS [Table Name], i.name AS [Index Name], i.index_id,
user_updates AS [Total Writes], user_seeks + user_scans + user_lookups AS [Total Reads],
user_updates - (user_seeks + user_scans + user_lookups) AS [Difference]
FROM sys.dm_db_index_usage_stats AS s WITH (NOLOCK)
INNER JOIN sys.indexes AS i WITH (NOLOCK)
ON s.[object_id] = i.[object_id]
AND i.index_id = s.index_id
WHERE OBJECTPROPERTY(s.[object_id],'IsUserTable') = 1
AND s.database_id = DB_ID()
AND user_updates > (user_seeks + user_scans + user_lookups)
AND i.index_id > 1
ORDER BY [Difference] DESC, [Total Writes] DESC, [Total Reads] ASC;

-- Look for indexes with high numbers of writes and zero or very low numbers of reads
-- Consider your complete workload
-- Investigate further before dropping an index

-- Missing Indexes current database by Index Advantage
SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS [index_advantage],
migs.last_user_seek, mid.[statement] AS [Database.Schema.Table],
mid.equality_columns, mid.inequality_columns, mid.included_columns,
migs.unique_compiles, migs.user_seeks, migs.avg_total_user_cost, migs.avg_user_impact
FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK)
INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK)
ON migs.group_handle = mig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK)
ON mig.index_handle = mid.index_handle
WHERE mid.database_id = DB_ID() -- Remove this to see for entire instance
ORDER BY index_advantage DESC;

-- Look at last user seek time, number of user seeks to help determine source and importance
-- SQL Server is overly eager to add included columns, so beware
-- Do not just blindly add indexes that show up from this query!!!

-- Breaks down buffers used by current database by object (table, index) in the buffer cache
SELECT OBJECT_NAME(p.[object_id]) AS [ObjectName],
p.index_id, COUNT(*)/128 AS [Buffer size(MB)],  COUNT(*) AS [BufferCount],
p.data_compression_desc AS [CompressionType]
FROM sys.allocation_units AS a
INNER JOIN sys.dm_os_buffer_descriptors AS b
ON a.allocation_unit_id = b.allocation_unit_id
INNER JOIN sys.partitions AS p
ON a.container_id = p.hobt_id
WHERE b.database_id = DB_ID()
AND p.[object_id] > 100
GROUP BY p.[object_id], p.index_id, p.data_compression_desc
ORDER BY [BufferCount] DESC;

-- Tells you what tables and indexes are using the most memory in the buffer cache

-- Get Table names, row counts, and compression status for clustered index or heap
SELECT OBJECT_NAME(object_id) AS [ObjectName],
SUM(Rows) AS [RowCount], data_compression_desc AS [CompressionType]
FROM sys.partitions
WHERE index_id < 2 --ignore the partitions from the non-clustered index if any
AND OBJECT_NAME(object_id) NOT LIKE 'sys%'
AND OBJECT_NAME(object_id) NOT LIKE 'queue_%'
AND OBJECT_NAME(object_id) NOT LIKE 'filestream_tombstone%'
GROUP BY object_id, data_compression_desc
ORDER BY SUM(Rows) DESC;

-- Gives you an idea of table sizes, and possible data compression opportunities

-- When were Statistics last updated on all indexes?
SELECT o.name, i.name AS [Index Name], 
      STATS_DATE(i.[object_id], i.index_id) AS [Statistics Date],
      s.auto_created, s.no_recompute, s.user_created, st.row_count
FROM sys.objects AS o WITH (NOLOCK)
INNER JOIN sys.indexes AS i WITH (NOLOCK)
ON o.[object_id] = i.[object_id]
INNER JOIN sys.stats AS s WITH (NOLOCK)
ON i.[object_id] = s.[object_id]
AND i.index_id = s.stats_id
INNER JOIN sys.dm_db_partition_stats AS st WITH (NOLOCK)
ON o.[object_id] = st.[object_id]
WHERE o.[type] = 'U'
ORDER BY STATS_DATE(i.[object_id], i.index_id) ASC;   

-- Helps discover possible problems with out-of-date statistics
-- Also gives you an idea which indexes are most active