PostgreSQL MSI ignores --datadir flag during minor upgrade on Windows

Hello,

Recently we tried to upgrade a client machine's PostgreSQL version from
15.13 to 15.16.
We often upgrade our client machines from versions 9/13 to 15 without
encountering any issues.
However, during this upgrade (15.13 --> 15.16) we've noticed that
post-upgrade the PostgreSQL service assigned data directory changed to the
default value "C:\Program Files\PostgreSQL\15\data".

Our client's data directory prior to the upgrade was
"F:\AidocData\PostgreSQL\15\data". This change caused data to be written to
the wrong location until we found the issue.

This is the command we use for the upgrade:

> Start-Process $installer_exe -ArgumentList "--unattendedmodeui minimal
> --mode unattended --superaccount $POSTGRES_ROOT_USER --superpassword
> $POSTGRES_ROOT_USER_PWD --serverport $port --datadir `"$data_dir`" --locale
> `"$locale_name`"" -Wait

I looked into your codebase and found that during an upgrade the installer
defaults to the Registry value for data directory and ignores the --datadir
flag I provided in my command.

In server/pgserver.xml.in, in the server component’s
preInstallationActionList:

*pgserver.xml.in <http://pgserver.xml.in>*
Lines 1142-1153

<!-- Set datadir if an existing installation is found -->
> <setInstallerVariable>
> <name>datadir</name>
> <value>${iDataDirectory}</value>
> <ruleList>
> <stringTest>
> <text>${iDataDirectory}</text>
> <type>not_empty</type>
> </stringTest>
> <isFalse value="${extract_mode}"/>
> </ruleList>
> </setInstallerVariable>

*iDataDirectory is read from the registry here:*
*pgserver.xml.in <http://pgserver.xml.in>*
Lines 1003-1008

<!-- Get the existing data directory. -->
> <registryGet>
> <name>Data Directory</name>
>
> <key>HKEY_LOCAL_MACHINE\SOFTWARE\PostgreSQL\Installations\postgresql${service_suffix}-${product_version}</key>
> <variable>iDataDirectory</variable>
> </registryGet>

*What goes wrong:*
When passing --datadir "F:\AidocData\PostgreSQL\15\data" on the command
line, the wizard sets datadir = "F:\AidocData\PostgreSQL\15\data".

Later, in preInstallationActionList, the installer reads iDataDirectory
from the registry.
If iDataDirectory is not empty, it overwrites datadir with that value.

1. There is no check that the user explicitly provided --datadir, so the
CLI value is ignored.

If the registry still has the old default path (e.g. C:\Program
Files\PostgreSQL\15\data), the service ends up re-registered with that path
instead of F:\AidocData\PostgreSQL\15\data.
When the registry can be wrong

- Initial install used the default data directory, then data was moved
to F:\AidocData\PostgreSQL\15\data and the service was updated manually,
but the PostgreSQL registry key was not.
- A previous install or reinstall wrote the default path to the registry.
- Any other case where the registry value does not match the actual data
location.

*Fix*
Only use the registry value when the user has not provided --datadir on the
command line. For example, add a condition so that datadir is set from
iDataDirectory only when datadir is empty:

<!-- Set datadir if an existing installation is found (only when user
> didn't provide --datadir) -->
> <setInstallerVariable>
> <name>datadir</name>
> <value>${iDataDirectory}</value>
> <ruleList>
> <stringTest>
> <text>${iDataDirectory}</text>
> <type>not_empty</type>
> </stringTest>
> <stringTest>
> <text>${datadir}</text>
> <type>empty</type>
> </stringTest>
> <isFalse value="${extract_mode}"/>
> </ruleList>
> </setInstallerVariable>

This keeps the current behavior when --datadir is not passed, but ensures
that an explicit --datadir is not overridden by the registry.

Please consider investigating this issue and its solution.
If I misunderstood anything please let me know. Thanks!
--

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Ben Caspi
DevOps Engineer

www.aidoc.com | benc(at)aidoc(dot)com

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