Database Level

use [<dbname>]
select * from sys.all_objects where name = 'BATCH_JOB_SEQ';

-- create the extended event session and start it
CREATE EVENT SESSION FailedLogins
ON SERVER
 ADD EVENT sqlserver.error_reported
 (
   ACTION 
   (
     sqlserver.client_app_name,
     sqlserver.client_hostname,
     sqlserver.nt_username
    )
    WHERE severity = 14
      AND state > 1
  )
  ADD TARGET package0.asynchronous_file_target
  (
    SET FILENAME = N'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQL\MSSQL\Log\xEventSessions\FailedLogins.xel',
    METADATAFILE = N'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQL\MSSQL\Log\xEventSessions\FailedLogins.xem'
  );
GO

ALTER EVENT SESSION FailedLogins ON SERVER
  STATE = START;
GO

-- Query the files
WITH event_data AS 
(
  SELECT data = CONVERT(XML, event_data)
    FROM sys.fn_xe_file_target_read_file(
   'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQL\MSSQL\Log\xEventSessions\FailedLogins*.xel', 
   'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQL\MSSQL\Log\xEventSessions\FailedLogins*.xem', 
   NULL, NULL
 )
),
tabular AS
(
  SELECT 
    [host] = data.value('(event/action[@name="client_hostname"]/value)[1]','nvarchar(4000)'),
    [app] = data.value('(event/action[@name="client_app_name"]/value)[1]','nvarchar(4000)'),
    [error] = data.value('(event/data[@name="error_number"]/value)[1]','int'),
    [state] = data.value('(event/data[@name="state"]/value)[1]','tinyint'),
    [message] = data.value('(event/data[@name="message"]/value)[1]','nvarchar(250)')
  FROM event_data
)
SELECT [host],[app],[state],[message],[date/time]
  FROM tabular
  WHERE error = 18456 
  ORDER BY [date/time] DESC;

Add Powershell dbatools module

Execute an elevated powershell session (Execute as administrator) and run the command:

Import-Module dbatools

Windows PowerShell
Copyright (C) 2016 Microsoft Corporation. All rights reserved.

Loading personal and system profiles took 756ms.
PS C:\WINDOWS\system32> Install-Module dbatools

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 'C:\Users\hell\AppData\Local\PackageManagement\ProviderAssemblies'. You can also install the NuGet provider by running 'Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Force'. Do you want
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Untrusted repository
You are installing the modules from an untrusted repository. If you trust this repository, change its InstallationPolicy value by running the Set-PSRepository cmdlet. Are you sure you want to install the
modules from 'PSGallery'?
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PS C:\WINDOWS\system32>

Security Aspects

This article Security Aspects by Chrissy Lemaire explains security-related issues (for the dbatools module and PowerShell in general).

select
[Average Duration (msec]=total_elapsed_time/execution_count/1000, 
creation_time,last_execution_time, 
execution_count from sys.dm_exec_query_stats
where plan_handle in 
(
SELECT plan_handle
FROM sys.dm_exec_cached_plans 
CROSS APPLY sys.dm_exec_sql_text(plan_handle)
CROSS APPLY sys.dm_exec_query_plan(plan_handle)
where text like '%<sql text>%'
)

SELECT UseCounts, Cacheobjtype, Objtype, TEXT, query_plan, plan_handle
FROM sys.dm_exec_cached_plans 
CROSS APPLY sys.dm_exec_sql_text(plan_handle)
CROSS APPLY sys.dm_exec_query_plan(plan_handle)
where text like '%<sql text>%'
order by text

DBCC FREEPROCCACHE(<plan_handle>)

SELECT DISTINCT
OBJECT_NAME(s.[object_id]) AS TableName,
c.name AS ColumnName,
s.name AS StatName,
s.auto_created,
s.user_created,
s.no_recompute,
s.[object_id],
s.stats_id,
sc.stats_column_id,
sc.column_id,
STATS_DATE(s.[object_id], s.stats_id) AS LastUpdated
FROM sys.stats s JOIN sys.stats_columns sc 
              ON sc.[object_id] = s.[object_id] AND sc.stats_id = s.stats_id
JOIN sys.columns c ON c.[object_id] = sc.[object_id] AND c.column_id = sc.column_id
JOIN sys.partitions par ON par.[object_id] = s.[object_id]
JOIN sys.objects obj ON par.[object_id] = obj.[object_id]
WHERE OBJECTPROPERTY(s.OBJECT_ID,'IsUserTable') = 1
AND (s.auto_created = 1 OR s.user_created = 1)
order by LastUpdated desc; 

sp_msforeachtable 'sp_autostats ''?'''

-- total buffer usage by database for current instance
WITH DB_CPU_Stats
AS
(SELECT DatabaseID, DB_Name(DatabaseID) AS [DatabaseName], SUM(total_worker_time) AS [CPU_Time_Ms]
 FROM sys.dm_exec_query_stats AS qs
 CROSS APPLY (SELECT CONVERT(int, value) AS [DatabaseID] 
              FROM sys.dm_exec_plan_attributes(qs.plan_handle)
              WHERE attribute = N'dbid') AS F_DB
 GROUP BY DatabaseID)
SELECT ROW_NUMBER() OVER(ORDER BY [CPU_Time_Ms] DESC) AS [row_num],
       DatabaseName, [CPU_Time_Ms], 
       CAST([CPU_Time_Ms] * 1.0 / SUM([CPU_Time_Ms]) OVER() * 100.0 AS DECIMAL(5, 2)) AS [CPUPercent]
FROM DB_CPU_Stats
WHERE DatabaseID > 4 -- system databases
AND DatabaseID <> 32767 -- ResourceDB
ORDER BY row_num OPTION (RECOMPILE);

-- Memory utilization by database
SELECT DB_NAME(database_id) AS [Database Name],
COUNT(*) * 8/1024.0 AS [Cached Size (MB)]
FROM sys.dm_os_buffer_descriptors
WHERE database_id > 4 -- system databases
AND database_id <> 32767 -- ResourceDB
GROUP BY DB_NAME(database_id)
ORDER BY [Cached Size (MB)] DESC OPTION (RECOMPILE);

To search for an object in all databases in a MS SQL Server Instance:

Link
Search for Object in all databases

When a SQL Server process is killed (kill spid), the non-commited work (transactions) will take a certain amount of time to roll back.

Use kill spid with statusonly to determine how much time a killed process will take to rollback

The transaction log is truncated when a transaction log backup is executed (recovery mode Full).

In an emergency situation, if the log becomes full and it is not possible to backup the log normally, it can be pseudo-backed-up to a fictitious location.

Use at your own risk and only do this if you know what you’re doing.

This will prevent the possibilty of point-in-time recovery, so a full backup should be done after this operation

BACKUP LOG <db name> TO DISK='NUL:'