/*
Source: https://www.sqlshack.com/insight-into-the-sql-server-buffer-cache/
Author: Ed Pollack
*/
WITH CTE_BUFFER_CACHE AS (
    SELECT
        objects.name AS object_name,
        objects.type_desc AS object_type_description,
        objects.object_id,
        COUNT(*) AS buffer_cache_pages,
        COUNT(*) * 8 / 1024  AS buffer_cache_used_MB
    FROM sys.dm_os_buffer_descriptors
    INNER JOIN sys.allocation_units
    ON allocation_units.allocation_unit_id = dm_os_buffer_descriptors.allocation_unit_id
    INNER JOIN sys.partitions
    ON ((allocation_units.container_id = partitions.hobt_id AND type IN (1,3))
    OR (allocation_units.container_id = partitions.partition_id AND type IN (2)))
    INNER JOIN sys.objects
    ON partitions.object_id = objects.object_id
    WHERE allocation_units.type IN (1,2,3)
    AND objects.is_ms_shipped = 0
    AND dm_os_buffer_descriptors.database_id = DB_ID()
    GROUP BY objects.name,
             objects.type_desc,
             objects.object_id)
SELECT
    PARTITION_STATS.name,
    CTE_BUFFER_CACHE.object_type_description,
    CTE_BUFFER_CACHE.buffer_cache_pages,
    CTE_BUFFER_CACHE.buffer_cache_used_MB,
    PARTITION_STATS.total_number_of_used_pages,
    PARTITION_STATS.total_number_of_used_pages * 8 / 1024 AS total_mb_used_by_object,
    CAST((CAST(CTE_BUFFER_CACHE.buffer_cache_pages AS DECIMAL) / CAST(PARTITION_STATS.total_number_of_used_pages AS DECIMAL) * 100) AS DECIMAL(5,2)) AS percent_of_pages_in_memory
FROM CTE_BUFFER_CACHE
INNER JOIN (
    SELECT 
        objects.name,
        objects.object_id,
        SUM(used_page_count) AS total_number_of_used_pages
    FROM sys.dm_db_partition_stats
    INNER JOIN sys.objects
    ON objects.object_id = dm_db_partition_stats.object_id
    WHERE objects.is_ms_shipped = 0
    GROUP BY objects.name, objects.object_id) PARTITION_STATS
ON PARTITION_STATS.object_id = CTE_BUFFER_CACHE.object_id
ORDER BY CAST(CTE_BUFFER_CACHE.buffer_cache_pages AS DECIMAL) / CAST(PARTITION_STATS.total_number_of_used_pages AS DECIMAL) DESC;

SELECT
    indexes.name AS index_name,
    objects.name AS object_name,
    objects.type_desc AS object_type_description,
    COUNT(*) AS buffer_cache_pages,
    COUNT(*) * 8 / 1024  AS buffer_cache_used_MB,
    SUM(allocation_units.used_pages) AS pages_in_index,
    SUM(allocation_units.used_pages) * 8 /1024 AS total_index_size_MB,
    CAST((CAST(COUNT(*) AS DECIMAL) / CAST(SUM(allocation_units.used_pages) AS DECIMAL) * 100) AS DECIMAL(5,2)) AS percent_of_pages_in_memory
FROM sys.dm_os_buffer_descriptors
INNER JOIN sys.allocation_units
ON allocation_units.allocation_unit_id = dm_os_buffer_descriptors.allocation_unit_id
INNER JOIN sys.partitions
ON ((allocation_units.container_id = partitions.hobt_id AND type IN (1,3))
OR (allocation_units.container_id = partitions.partition_id AND type IN (2)))
INNER JOIN sys.objects
ON partitions.object_id = objects.object_id
INNER JOIN sys.indexes
ON objects.object_id = indexes.object_id
AND partitions.index_id = indexes.index_id
WHERE allocation_units.type IN (1,2,3)
AND objects.is_ms_shipped = 0
AND dm_os_buffer_descriptors.database_id = DB_ID()
GROUP BY indexes.name,
         objects.name,
         objects.type_desc
ORDER BY CAST((CAST(COUNT(*) AS DECIMAL) / CAST(SUM(allocation_units.used_pages) AS DECIMAL) * 100) AS DECIMAL(5,2)) DESC;

WITH CTE_BUFFER_CACHE AS
( SELECT
  databases.name AS database_name,
  COUNT(*) AS total_number_of_used_pages,
  CAST(COUNT(*) * 8 AS DECIMAL) / 1024 AS buffer_cache_total_MB,
  CAST(CAST(SUM(CAST(dm_os_buffer_descriptors.free_space_in_bytes AS BIGINT)) AS DECIMAL) / (1024 * 1024) AS DECIMAL(20,2))  AS buffer_cache_free_space_in_MB
 FROM sys.dm_os_buffer_descriptors
 INNER JOIN sys.databases
 ON databases.database_id = dm_os_buffer_descriptors.database_id
 GROUP BY databases.name)
SELECT
 *,
 CAST((buffer_cache_free_space_in_MB / NULLIF(buffer_cache_total_MB, 0)) * 100 AS DECIMAL(5,2)) AS buffer_cache_percent_free_space
FROM CTE_BUFFER_CACHE
ORDER BY buffer_cache_free_space_in_MB / NULLIF(buffer_cache_total_MB, 0) DESC;

SELECT
    objects.name AS object_name,
    objects.type_desc AS object_type_description,
    COUNT(*) AS buffer_cache_pages,
    CAST(COUNT(*) * 8 AS DECIMAL) / 1024  AS buffer_cache_total_MB,
    CAST(SUM(CAST(dm_os_buffer_descriptors.free_space_in_bytes AS BIGINT)) AS DECIMAL) / 1024 / 1024 AS buffer_cache_free_space_in_MB,
    CAST((CAST(SUM(CAST(dm_os_buffer_descriptors.free_space_in_bytes AS BIGINT)) AS DECIMAL) / 1024 / 1024) / (CAST(COUNT(*) * 8 AS DECIMAL) / 1024) * 100 AS DECIMAL(5,2)) AS buffer_cache_percent_free_space
FROM sys.dm_os_buffer_descriptors
INNER JOIN sys.allocation_units
ON allocation_units.allocation_unit_id = dm_os_buffer_descriptors.allocation_unit_id
INNER JOIN sys.partitions
ON ((allocation_units.container_id = partitions.hobt_id AND type IN (1,3))
OR (allocation_units.container_id = partitions.partition_id AND type IN (2)))
INNER JOIN sys.objects
ON partitions.object_id = objects.object_id
WHERE allocation_units.type IN (1,2,3)
AND objects.is_ms_shipped = 0
AND dm_os_buffer_descriptors.database_id = DB_ID()
GROUP BY objects.name,
            objects.type_desc,
            objects.object_id
HAVING COUNT(*) > 0
ORDER BY COUNT(*) DESC;

SELECT
    databases.name AS database_name,
    COUNT(*) AS buffer_cache_total_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 1
                ELSE 0
        END) AS buffer_cache_dirty_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 0
                ELSE 1
        END) AS buffer_cache_clean_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 1
                ELSE 0
        END) * 8 / 1024 AS buffer_cache_dirty_page_MB,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 0
                ELSE 1
        END) * 8 / 1024 AS buffer_cache_clean_page_MB
FROM sys.dm_os_buffer_descriptors
INNER JOIN sys.databases
ON dm_os_buffer_descriptors.database_id = databases.database_id
GROUP BY databases.name;


SELECT
    indexes.name AS index_name,
    objects.name AS object_name,
    objects.type_desc AS object_type_description,
    COUNT(*) AS buffer_cache_total_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 1
                ELSE 0
        END) AS buffer_cache_dirty_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 0
                ELSE 1
        END) AS buffer_cache_clean_pages,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 1
                ELSE 0
        END) * 8 / 1024 AS buffer_cache_dirty_page_MB,
    SUM(CASE WHEN dm_os_buffer_descriptors.is_modified = 1
                THEN 0
                ELSE 1
        END) * 8 / 1024 AS buffer_cache_clean_page_MB
FROM sys.dm_os_buffer_descriptors
INNER JOIN sys.allocation_units
ON allocation_units.allocation_unit_id = dm_os_buffer_descriptors.allocation_unit_id
INNER JOIN sys.partitions
ON ((allocation_units.container_id = partitions.hobt_id AND type IN (1,3))
OR (allocation_units.container_id = partitions.partition_id AND type IN (2)))
INNER JOIN sys.objects
ON partitions.object_id = objects.object_id
INNER JOIN sys.indexes
ON objects.object_id = indexes.object_id
AND partitions.index_id = indexes.index_id
WHERE allocation_units.type IN (1,2,3)
AND objects.is_ms_shipped = 0
AND dm_os_buffer_descriptors.database_id = DB_ID()
GROUP BY indexes.name,
         objects.name,
         objects.type_desc
ORDER BY COUNT(*) DESC;


-- Page Life Expectancy
SELECT *
FROM sys.dm_os_performance_counters
WHERE dm_os_performance_counters.object_name LIKE '%Buffer Manager%'
AND dm_os_performance_counters.counter_name = 'Page life expectancy';


-- If your server has a NUMA (non-uniform memory access) architecture
SELECT *
FROM sys.dm_os_performance_counters
WHERE dm_os_performance_counters.object_name LIKE '%Buffer Node%'
AND dm_os_performance_counters.counter_name = 'Page life expectancy';