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how_to:database_issues [2013/06/24 08:35] – [PostgreSQL service not starting] paulhow_to:database_issues [2013/08/30 12:36] – paul
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 VPOP3 version 3 and later use the [[http://www.postgresql.org|PostgreSQL]]] database server. This is an open source enterprise level database server. Several VPOP3 problems are due to problems with the database service. VPOP3 version 3 and later use the [[http://www.postgresql.org|PostgreSQL]]] database server. This is an open source enterprise level database server. Several VPOP3 problems are due to problems with the database service.
  
-=====Disk Caching===== +  * [[Database & Disk Caching]] 
- +  * [[Software conflicting with database]] 
-One key point is that, like all other high-end databases, PostgreSQL should not be run on a server with disk level [[http://en.wikipedia.org/wiki/Cache#Operation|write back caching]]. With write back caching, the disk will report data as being written to disk when it is still in the disk's cache memory. If the power then fails, this data is lost and can cause database corruption. As long as the database server really knows when the data has been written to disk, power failure will not cause database corruption as it can be automatically recovered after a power failure. +  * [[VPOP3DB/PostgreSQL service not starting|VPOP3DB Service not starting]]
- +
-High-end RAID controllers often contain a battery backed write cache (BBWC) - in this case, if the power fails, the cached data is held in battery powered memory until the power is restored. After power is restored the cached data will be written to disk. In this case, using write back caching through the BBWC is perfectly safe (as long as power is not left off for so long that the batteries run down). +
- +
-It is slightly less safe, but still usually OK, to have a UPS with automated shutdown of the PC. You still have to ensure that the PC is not just turned off without shutting down properly. +
- +
-If you don't have either of these facilities, then make sure you turn off write-back caching in Windows. (Note that 'Server' versions of Windows will usually have write-back caching disabled by default, because they often store critical data and run database servers, and 'Desktop' versions of Windows will usually have write-back caching enabled by default, because their data is usually less critical, and speed is considered more important than reliability). +
- +
-Exactly how you turn off write-back caching depends on your version of Windows, and the disk controller. +
- +
-The instructions below are for Windows 7 with standard SATA disks +
- +
-  - Go to the 'Device Manager' in Windows. In Windows 7 this is via **Control Panel -> System -> Device Manager**\\ {{:how_to:device_manager.png|}} +
-  - Under **Disk Drives** find the hard disk that VPOP3 is installed on, and right-click it and choose **Properties**\\ {{:how_to:disk_properties.png|}} +
-  - Go to the **Policies** tab. Turn off **Enable write caching onthe device** and press **OK**\\ {{:how_to:write_caching.png|}} +
- +
-=====Possible Conflicting Software===== +
-We strongly recommend that virus scanners exclude the VPOP3\pgsql\data folder and all subfolders. If a virus scanner decides to quarantine a file from within this folder structure, that can cause VPOP3 not to run, and could lead to data loss or corruption. +
- +
-We also recommend that backup software does not backup this folder structure. If a backup program opens a file for backup, and then the database server needs it, it can cause problems, and crashes.+
  
 =====Database corruption===== =====Database corruption=====
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 ====Event Viewer Entries==== ====Event Viewer Entries====
 +In the Windows Event Viewer, view the //Application// event log, then look for **Error** entries for the **PostgreSQL** source.
 +
 +Depending on your installation, the events may all be displayed as something like:
 +  The description for Event ID xxxx from source PostgreSQL cannot be found. Either the component that raises this event is not installed on your local computer....
 +  
 +If that's the case, don't worry, just look lower down in the event message. It will say something like 
 +  The following information was included with the event
 +  
 +It is that information you need to see. Some possible event messages we have seen are:
 +  
 +===pg_ctl: this data directory appears to be running a pre-existing postmaster===
 +If this is the case, then usually it means that a previous attempt to start PostgreSQL was made, but it timed out or something, and is now in a 'partially' running state. 
 +
 +To solve this, go to Windows TaskManager (Ctrl-Alt-Del - choose TaskManager), then go to the **Processes** tab and click **Show processes for all users**. Sort by **Image Name**, and **End Process** on all the **postgres.exe** processes. Once those are all ended, then you should be able to start the **VPOP3DB** service manually.
 ====PostgreSQL Log Entries==== ====PostgreSQL Log Entries====
-If you get **FATAL** entries in the PostgreSQL log files (in **VPOP3\pgsql\data\pg_log**) then they may give more information about why PostgreSQL could not start. Some log entries we have come across are below.+If you get **FATAL** or **PANIC** entries in the PostgreSQL log files (in **VPOP3\pgsql\data\pg_log**) then they may give more information about why PostgreSQL could not start. Some log entries we have come across are below.
  
 ===no pg_hba.conf entry for host "::1", user "postgres", database "postgres"=== ===no pg_hba.conf entry for host "::1", user "postgres", database "postgres"===
how_to/database_issues.txt · Last modified: 2018/11/14 10:45 by 127.0.0.1

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