Snippet Name: Buffer_latch_timeout_fix

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Created Date: 2025-06-16 13:12:39
Last Modified Date: 2025-05-31 10:32:20

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Title: Buffer latch timeout fix
Author: user
in sql server 2019, my log is filled with errors similar to this: A time-out occurred while waiting for buffer latch -- type 2, bp 000002D00ED7BAC0, page 28:12227542, stat 0x9, database id: 21, allocation unit Id: 72057931369480192, task 0x00000191C605FC28 : 0, waittime 300 seconds, flags 0xfffffffffffff038, owning task 0x0000000000000000. Not continuing to wait.

Author: ChatGPT
That error in SQL Server 2019 is a **buffer latch timeout**, which usually indicates **I/O contention**, **heavy memory pressure**, or **prolonged blocking** involving data pages. Here's a breakdown and what you can do about it.

---

### ???? Error Breakdown:
```
A time-out occurred while waiting for buffer latch
-- type 2 (BUF_LOCK_EX = Exclusive)
page 28:12227542 (File 28, Page 12227542)
database id: 21
allocation unit Id: 72057931369480192
waittime 300 seconds
```

- **Buffer latch type 2**: Exclusive latch ??? typically when a page is being modified.
- **Page 28:12227542**: File ID 28, page 12227542 ??? indicates where the contention is.
- **Waittime 300 seconds**: The task waited 5 minutes, then gave up.
- **Database ID 21**: You can map this to the actual DB name using `DB_NAME(21)`.

---

### ???? Steps to Diagnose and Fix

#### 1. **Find the Table/Index from the Page**
Use the `DBCC PAGE` and `sys.allocation_units` to get more info:

```sql
USE [YourDatabaseName];
DBCC TRACEON(3604);
DBCC PAGE(21, 1, 12227542, 3);  -- DB ID, file ID, page ID, print option
```

- Look for `Metadata: ObjectId`, IndexId, and PartitionId.
- Then use this to find the table:

```sql
SELECT OBJECT_NAME([object_id]), * 
FROM sys.partitions 
WHERE hobt_id = [hobt_id_from_dbcc_page];
```

Or use allocation unit to backtrack:

```sql
SELECT OBJECT_NAME(p.object_id) AS TableName, au.type_desc, au.total_pages
FROM sys.allocation_units au
JOIN sys.partitions p ON au.container_id = p.hobt_id
WHERE au.allocation_unit_id = 72057931369480192;
```

---

#### 2. **Check for Blocking/Deadlocks**
Check the system health session for blocking chains:

```sql
SELECT * 
FROM sys.dm_exec_requests 
WHERE blocking_session_id <> 0;
```

Or use Extended Events:
```sql
-- Look for latch_wait and latch_suspend_end events
-- Or use the system_health session preconfigured in XE
```

---

#### 3. **Check Disk I/O and Memory Pressure**
These timeouts can indicate SQL Server is overwhelmed:

- Run this to get IO stats:
```sql
SELECT DB_NAME(database_id) AS DBName, file_id, io_stall, num_of_reads, num_of_writes
FROM sys.dm_io_virtual_file_stats(NULL, NULL);
```

- Memory pressure? Look at:
```sql
SELECT *
FROM sys.dm_os_memory_clerks
ORDER BY pages_kb DESC;
```

---

#### 4. **Review Waits**
Latch timeouts correspond to `PAGEIOLATCH_EX` or `PAGELATCH_EX` waits:

```sql
SELECT wait_type, wait_time_ms, waiting_tasks_count
FROM sys.dm_os_wait_stats
WHERE wait_type LIKE 'PAGEIOLATCH%' OR wait_type LIKE 'PAGELATCH%'
ORDER BY wait_time_ms DESC;
```

---

### ??? Suggestions
- **Rebuild fragmented indexes** on the affected table.
- **Update statistics** on large tables.
- **Check for long-running transactions** that are keeping latches.
- **Look for hot pages** (frequent updates to the same row/page).
- If the page is part of a **heavily updated index**, consider **row-level versioning** (RCSI).
- Consider adding **more memory** or **faster disk** if you???re consistently IO-bound.

---

If you're seeing this for **tempdb** (common for latch contention), there are additional mitigation strategies like:

- Adding multiple tempdb files (same size, autogrowth).
- Setting `TF 1118` (pre-SQL 2016 behavior).

Let me know the result of the queries and what database or table/page is being affected, and I can help you dive deeper.