Chapter 1: System Procedures

sp_cacheconfig

Description

Creates, configures, reconfigures, and drops data caches, and provides information about them.

Syntax

sp_cacheconfig [cachename [ ,"cache_size[P|K|M|G]" ] 
	[,logonly | mixed ] [,strict | relaxed ] ]
	[, "cache_partition=[1|2|4|8|16|32|64]"]

Parameters

cachename: is the name of the data cache to be created or configured. Cache names must be unique, and can be up to 30 characters long. A cache name does not have to be a valid Adaptive Server identifier, that is, it can contain spaces and other special characters.

cache_size: is the size of the data cache to be created or, if the cache already exists, the new size of the data cache. The minimum size of a cache is 256 times the logical page size of the server. Size units can be specified with P for pages, K for kilobytes, M for megabytes, or G for gigabytes. The default is K. For megabytes and gigabytes, you can specify floating-point values. The cache size is in multiples of the logical page size.

logonly | mixed: specifies the type of cache.

strict | relaxed: specifies the cache replacement policy.

cache_partition: specifies the number of partitions to create in the cache.

Examples

Example 1

Creates the data cache pub_cache with 10MB of space. All space is in the default logical page size memory pool:

sp_cacheconfig pub_cache, "10M"

Example 2

Reports the current configuration of pub_cache and any memory pools in the cache:

sp_cacheconfig pub_cache

Example 3

Drops pub_cache at the next start of Adaptive Server:

sp_cacheconfig pub_cache, "0"

Example 4

Creates pub_log_cache and sets its type to logonly in a single step:

sp_cacheconfig pub_log_cache, "2000K", logonly

Example 5

The first command creates the cache pub_log_cache with the default type mixed. The second command changes its status to logonly. The resulting configuration is the same as that in example 4:

sp_cacheconfig pub_log_cache, "2000K"
sp_cacheconfig pub_log_cache, logonly

Example 6

Creates a cache and sets the size, type, replacement policy and number of cache partitions:

sp_cacheconfig 'newcache', '50M', mixed, strict, "cache_partition=2"

Usage

The minimum cache size is 256 times the logical page size. For example, a 4K server would have a minimum cache size of 1024K.
If Adaptive Server is unable to allocate all the memory requested while you are creating a new cache or adding memory to an existing cache, it allocates all the available memory. However, this additional memory is allocated at the next reboot of Adaptive Server.
If there are objects bound to cache (including the default cache), you cannot delete the cache until you unbind the objects.

Some of the actions you perform with sp_cacheconfig are dynamic (do not require a reboot of Adaptive Server) and some are static (require a reboot). Table 1-7 describes which are dynamic and which are static:

**Table 1-7: Dynamic and static sp_cacheconfig actions**
Dynamic sp_cacheconfig actions	Static sp_cacheconfig actions
Adding a new cache	Changing the number of cache partitions
Adding memory to an existing cache	Reducing a cache size
Deleting a cache	Changing the replacement policy
Changing a cache type

When you first create a data cache:
- All space is allocated to the logical page size memory pool.
- The default type is mixed.
Figure 1-1 shows a data cache for a 2K server with two user-defined data caches configured and the following pools:
- The default data cache with a 2K pool and a 16K pool
- A user cache with a 2K pool and a 16K pool
- A log cache with a 2K pool and a 4K pool
  
  Figure 1-1: Data cache with default and user-defined caches
The default data cache must always have the type default, and no other cache can have the type default.
The Adaptive Server housekeeper task does not do any buffer washing in caches with a type of logonly or in caches with a relaxed LRU replacement policy.

The following commands perform only 2K I/O: disk init, some dbcc commands, and drop table. The dbcc checkdb and dbcc checktable commands can perform large I/O for tables, but perform 2K I/O on indexes. Table 1-8 shows cache usage, depending on the binding of the database or object.

**Table 1-8: Cache usage for Transact-SQL commands**
Command	Database bound	Table or index is bound	Database or object not bound
create index	Bound cache	N/A	Default data cache
disk init	N/A	N/A	Default data cache
dbcc checkdb	Bound cache	N/A	Default data cache
dbcc checktable, indexalloc, tablealloc	Bound cache	Bound cache	Default data cache
drop table	Bound cache	Bound cache	Default data cache

Recovery uses only the logical page size pool of the default data cache. All pages for all transactions that must be rolled back or rolled forward are read into and changed in this pool. Be sure that your default logical page size pool is large enough for these transactions.

When you use sp_cacheconfig with no parameters, it reports information about all of the caches on the server. If you specify only a cache name, it reports information about only the specified cache. If you use a fragment of a cache name, it reports information for all names matching “%fragment%”.

All reports include a block of information that reports information about caches, and a separate block of data for each cache that provides information about the pools within the cache.

The output below, from a server using 2K, shows the configuration for:

The default data cache with two pools: a 2K pool and a 16K pool. The default data cache has 2 partitions.
pubs_cache with two pools: 2K and 16K

pubs_log, with the type set to logonly and cache replacement policy set to relaxed, with a 2K pool and a 4K pool

Cache Name               Status    Type     Config Value  Run Value
 ----------------------- --------- -------- ------------ --------
default data cache        Active   Default      0.00 Mb   26.09 Mb 
pubs_cache               Active    Mixed        10.00 Mb  10.00 Mb 
pubs_log                 Active    Log Only      2.40 Mb    2.40 M
                                              ------------- --------
                                      Total     12.40 Mb   38.49 Mb
===================================================================
Cache: default data cache,   Status: Active,   Type: Default
      Config Size: 0.00 Mb,   Run Size: 26.09 Mb
      Config Replacement: strict LRU,   Run Replacement: strict LRU
      Config Partition:            2,   Run Partition:            2
 IO Size  Wash Size Config Size  Run Size     APF Percent 
 -------- --------- ------------ ------------ ----------- 
     2 Kb   3704 Kb      0.00 Mb     18.09 Mb     10
    16 Kb   1632 Kb      8.00 Mb      8.00 Mb     10
===================================================================
Cache: pubs_cache,   Status: Active,   Type: Mixed
      Config Size: 10.00 Mb,   Run Size: 10.00 Mb
      Config Replacement: strict LRU,   Run Replacement: strict LRU
      Config Partition:            1,   Run Partition:            1
 IO Size  Wash Size Config Size  Run Size     APF Percent 
 -------- --------- ------------ ------------ ----------- 
     2 Kb   1228 Kb      0.00 Mb      6.00 Mb     10
    16 Kb    816 Kb      4.00 Mb      4.00 Mb     10
===================================================================
Cache: pubs_log,   Status: Active,   Type: Log Only
      Config Size: 2.40 Mb,   Run Size: 2.40 Mb
      Config Replacement: relaxed LRU,   Run Replacement: relaxed LRU
      Config Partition:            1,   Run Partition:            1
 IO Size  Wash Size Config Size  Run Size     APF Percent 
 -------- --------- ------------ ------------ ----------- 
     2 Kb    206 Kb      0.00 Mb      1.01 Mb     10
    16 Kb    272 Kb      1.40 Mb      1.39 Mb     10

Table 1-9 lists the meaning of the columns in the output:

**Table 1-9: sp_cacheconfig output**
Column	Meaning
Cache Name	The name of the cache.
Status	One of the following: “Active” “Pend/Act” “Pend/Del” These are explained following this table.
Type	“Mixed” or “Log Only” for user-defined caches, “Default” for the default data cache.
I/O Size	The size of I/O for a memory pool. This column is blank on the line that shows that cache configuration.
Wash Size	The size of the wash area for the pool. As pages enter the wash area of the cache, they are written to disk. This column is blank on the line that shows the cache configuration.
Config Value or Config Size	The size that the cache or pool. If the value is 0, the size has not been explicitly configured, and a default value will be used.
Run Value or Run Size	The size of the cache or pool now in use on Adaptive Server.
Config/ Run Replacement	The cache policy (strict or relaxed) that will be used for the cache after the next restart, and the current replacement policy. These will be different only if the policy has been changed since the last reboot.
Config/Run Partition	The number of cache partitions that will be used for the cache, and the current number of partitions. These will be different if sp_cacheconfig has been used to change the number of partitions since the last reboot.
APF Percent	The percentage of buffers in the pool that can hold buffers that have been fetched by asynchronous prefetch, but have not been used.
Total	The total size of data cache, if the report covers all caches, or the current size of the particular cache, if you specify a cache name.

The status “Pend” is short for pending. It always occurs in combination with either “Act” for Active or “Del” for Delete. It indicates that a configuration action has taken place, but that the server must be restarted in order for the changes to take effect.

Figure 1-2: Effects of restarts and sp_cacheconfig on cache status

This figure shows the effects of restarts and sp_cacheconfig on cache status.

You can also configure caches and pools by editing the configuration file. For more information, see the System Administration Guide.

Data cache memory

When Adaptive Server is first installed, all data cache memory is assigned to the logical page size pool of the cache named default data cache. The default data cache is used by all objects that are not explicitly bound to a data cache with sp_bindcache or whose databases are not bound to a cache.
When you create data caches, the memory allocation is validated against max memory. Memory for caches is allocated out of the memory allocated to Adaptive Server with the total logical_memory configuration parameter. To increase the amount of space available for caches, increase total logical memory, or decrease other configuration settings that use memory. If the sum of total logical memory and additional memory requested is greater than max memory, then Adaptive Server issues and error and does not perform the changes.

The default cache is used for all objects, including system tables, that are not bound to another cache, and is the only cache used during recovery. For more information, see the System Administration Guide.
A data cache requires a small percentage of overhead for structures that manage the cache. All cache overhead is taken from the default data cache. To see the amount of overhead required for a specific size of cache, use sp_helpcache, giving the size:
```
sp_helpcache "200M"
```
```
10.38Mb of overhead memory will be needed to manage a cache of size 200M
```
This is only an estimate of the overhead. The actual overhead may be larger because of runtime issues.

Changing existing caches

To change the size of an existing cache, specify the cache’s name and the new size.
- If you increase the size of an existing cache, all of the added space is placed in the smallest pool.
- To reduce the size of an existing cache, all of the space must be available in the logical page size pool. You may need to use sp_poolconfig to move space from other pools to this pool.
If you have a database or any nonlog objects bound to a cache, you cannot change its type to logonly.

Using cache partitions

Cache partitions can be used to reduce cache spinlock contention without needing to create separate caches and bind database objects to them. For more information on monitoring cache spinlock contention, see the Performance and Tuning Guide.
You can set the default number of cache partitions for all caches with the configuration parameter global cache partition number. See the System Administration Guide.

Dropping caches

To drop or delete a data cache, change its size to 0, as shown in example 3. When you set a cache’s size to 0, the cache is marked for deletion. The cache remains active, and all objects that are bound to that cache continue to use it.

You cannot drop the default data cache.
If you delete a data cache, and there are objects bound to the cache, the cache is left as-is in memory and Adaptive Server issues the following message:
```
Cache (nmc3) not deleted dynamically. Objects are bound to the cache. Use sp_unbindcache_all to unbind all objects bound to the cache.
```
The entry corresponding to the cache in the configuration file is deleted, as well as the entries corresponding to the cache in sysconfigures, and the cache is deleted the next time Adaptive Server is restarted.
You cannot run sp_cacheconfig within a transaction.

Permissions

Only a System Administrator can execute sp_cacheconfig to change cache configurations. Any user can execute sp_cacheconfig to view cache configurations.

Auditing

Values in event and extrainfo columns from the sysaudits table are:

Event	Audit option	Command or access audited	Information in extrainfo
38	exec_procedure	Execution of a procedure	Roles – Current active roles Keywords or options – NULL Previous value – NULL Current value – NULL Other information – All input parameters Proxy information – Original login name, if set proxy in effect