Fix Get-DbaDbTable performance regression

[potatoqualitee]

Resubmit PR from @PeterSawatzki-MGGM which keeps his commits but hopefully is able to merge.

Fix Get-DbaDbTable performance regression when using -Schema or -Table parameters

The ClearAndInitialize optimization introduced in 2.7.7 loads ALL tables in the database before filtering client-side. This causes severe performance issues (30+ seconds vs <1 second) when only specific tables are requested.

This fix adds server-side filtering by passing an XPath-style URN filter to ClearAndInitialize when -Schema or -Table parameters are specified.

Example filter: [@Schema='dispo' and @name='t_auftraege']

Performance improvement:

• Before: ~30 seconds (loads 1000+ tables)
• After: <1 second (loads only requested table)

Type of Change

• Bug fix (non-breaking change, fixes performance regression in 2.7.7)
• New feature (non-breaking change, adds functionality)
• Breaking change (affects multiple commands or functionality)
• Ran manual Pester test and has passed (Invoke-ManualPester)
• Adding code coverage to existing functionality
• Pester test is included
• If new file reference added for test, has is been added to github.com/dataplat/appveyor-lab ?
• Unit test is included
• Documentation
• Build system

Purpose

Fix a severe performance regression introduced in version 2.7.7 where Get-DbaDbTable with -Schema or -Table parameters loads ALL tables in the database before filtering client-side, causing execution times to increase from <1 second to 30+ seconds on databases with many tables.

Approach

The ClearAndInitialize optimization added in 2.7.7 uses an empty filter string, which causes SMO to load all tables:

$db.Tables.ClearAndInitialize('', [string[]]$properties)

This fix constructs an XPath-style URN filter when -Schema or -Table parameters are specified, enabling server-side filtering:

# Example: -Schema "dispo" -Table "t_auftraege"
$db.Tables.ClearAndInitialize("[@Schema='dispo' and @Name='t_auftraege']", [string[]]$properties)

The filter syntax follows the SMO ClearAndInitialize documentation.

Commands to test

# Test with -Schema and -Table (should be fast now)
Measure-Command { Get-DbaDbTable -SqlInstance $server -Database "YourDB" -Schema "dbo" -Table "YourTable" -Verbose }

# Test with -Schema only
Measure-Command { Get-DbaDbTable -SqlInstance $server -Database "YourDB" -Schema "dbo" -Verbose }

# Test with -Table only
Measure-Command { Get-DbaDbTable -SqlInstance $server -Database "YourDB" -Table "YourTable" -Verbose }

# Test without filters (unchanged behavior - loads all tables)
Measure-Command { Get-DbaDbTable -SqlInstance $server -Database "YourDB" }

# Test with multiple schemas
Get-DbaDbTable -SqlInstance $server -Database "YourDB" -Schema "dbo","sys" -Verbose

Screenshots

SQL Server Profiler comparison:

Metric	2.7.6 (fast)	2.7.7 (slow)	With Fix
Trace file size	88 KB	4,981 KB	~88 KB
Queries to sys.tables	1	1,150	1
Queries to sys.partitions	0	1,146	0
Execution time	<1 sec	~30 sec	<1 sec

Learning

• SMO's ClearAndInitialize method accepts an XPath-style filter as the first parameter
• The filter syntax uses [@Property='value'] format with and/or operators
• Documentation: https://learn.microsoft.com/en-us/dotnet/api/microsoft.sqlserver.management.smo.smocollectionbase.clearandinitialize

[potatoqualitee]

This somehow fixed the other branch. I don't know but I'll close it after merging his changes.

[PeterSawatzki-MGGM]

Thanks looking forward to it.