# Managing Plancache Memory and Disk Usage Compiled query plan images, sometimes referred to as 'modules' or 'code modules', are stored in a plancache for later use. The plancache consists of both an in-memory plancache and an on-disk plancache, also known as the persistent plancache or PPC. Thus, the plancache incrementally consumes both memory and disk storage space. This topic addresses managing that memory and storage space. Refer to [Code Generation](https://docs.singlestore.com/cloud/query-data/advanced-query-topics/code-generation.md) for more information on the plancache. Compiled query plan images may be removed from the in-memory plancache through expiration or eviction. A plan expires from the in-memory plancache (called expiration) after the time interval specified by the `plan_expiration_minutes` engine variable has elapsed. When a plan expires from the in-memory plan cache, the plan is removed fully from the in-memory plancache so when that plan is used again it must be fully reloaded from disk. Plans are evicted from the in-memory plan cache (called eviction) when the plancache memory usage goes over the thresholds specified by `compiled_images_eviction_memory_limit_mb` and `compiled_images_eviction_memory_limit_percent`, as described below. Once the plancache goes over the threshold, the engine evicts the least recently used query plan images until the memory use of the plancache falls below the threshold. Whether a plan expires or is evicted from the in-memory plancache, that plan remains in the on-disk plancache and is loaded back into memory the next time the query is run. Evicted plans will reload more quickly than expired plans, but in neither case will the plan be recompiled. Further, when a node restarts, the in-memory plancache starts off empty and plans are loaded back in from the on-disk plancache as queries are run. Query plans expire from the on-disk plancache as described in [Set Plan Expiration Limits](https://docs.singlestore.com/#UUID-d28dbae3-2336-1ac1-e97d-83832be8662a.md). When a plan expires from the on-disk plancache, it is completely removed from the plancache, and the query must be recompiled when it is run again. Query plans can be manually removed from the in-memory plancache as described in [Drop Plans from the Plancache](https://docs.singlestore.com/#UUID-fc252a59-15ea-15a6-9fe0-352241d148b0.md). All plans can be removed from the in-memory and on-disk plancache as described in [Drop All Plans from the Plancache](https://docs.singlestore.com/#section-idm234875781961294.md). ## Set Plan Expiration Limits Plancache expiration policy can be set through the `plan_expiration_minutes` and `disk_plan_expiration_minutes` engine variables. Expiration for the in-memory and on-disk plancaches is always enabled. Plans will expire from the on-disk plancache if the following conditions are met:  * The time limit specified by `disk_plan_expiration_minutes` is reached (assuming the plan has not been read from disk during that time), and * The plan is not in the in-memory plancache. This process also applies to temporary (temp) tables. SingleStore recommends reusing the same name for temporary tables to the degree possible. The following example shows how to set these variables to change the in-memory expiration limit to eight hours and set the on-disk expiration to one week. ```sql SHOW VARIABLES LIKE '%plan_expiration%'; ``` ```output +------------------------------+-------+ | Variable_name | Value | +------------------------------+-------+ | disk_plan_expiration_minutes | 20160 | | enable_disk_plan_expiration | ON | | plan_expiration_minutes | 720 | +------------------------------+-------+ 3 rows in set (0.08 sec) ``` ```sql SET GLOBAL plan_expiration_minutes = 480; ``` ```output Query OK, 0 rows affected (0.07 sec) ``` ```sql SET GLOBAL disk_plan_expiration_minutes = 10080; ``` ```output Query OK, 0 rows affected (0.09 sec) ``` ```sql SHOW VARIABLES LIKE '%plan_expiration%'; ``` ```output +------------------------------+-------+ | Variable_name | Value | +------------------------------+-------+ | disk_plan_expiration_minutes | 10080 | | enable_disk_plan_expiration | ON | | plan_expiration_minutes | 480 | +------------------------------+-------+ 3 rows in set (0.07 sec) ``` ## Manage Eviction of Compiled Query Plans > **📝 Note**: Plan eviction and the information in this section is applicable when `interpreter_mode` is set to `interpret_first` or `compile`. Compiled query plan images (sometimes referred to as 'modules' or 'code modules') are evicted using LRU (least-recently used) when the in-memory plancache reaches a set memory limit. The `compiled_images_eviction_memory_limit_percent` and `compiled_images_eviction_memory_limit_mb` variables are used to specify the memory limit available for caching query plan images. Query plan images are evicted when the `enable_compiled_images_eviction` engine variable is set to `ON`, which is the default setting. If the `compiled_images_eviction_memory_limit_percent` and `compiled_images_eviction_memory_limit_mb` variables are not set or are set to `0`, `compiled_images_eviction_memory_limit_percent` will be set as a percentage of `maximum_memory` as shown in the following table. | `maximum_memory`(GB) | `compiled_images_eviction_memory_limit_percent`Value | In-memory Plancache Memory Limit | | -------------------- | ---------------------------------------------------- | -------------------------------- | | 0-1 | Prohibited (`maximum_memory`minimum is 1GB) | | | 1-64 | `10` | 10% of`maximum_memory` | | 64+ | `5` | 5% of`maximum_memory` | If the `compiled_images_eviction_memory_limit_mb` or `compiled_images_eviction_memory_limit_percent` variables are set, the memory limit for the in-memory plancache is derived at runtime as shown in the following table. The notation **`_mb`** denotes `compiled_images_eviction_memory_limit_mb` and **`_percent`** denotes `compiled_images_eviction_memory_limit_percent`. | \_percent | \_mb | In-memory Plancache Memory Limit | | --------- | --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- | | 0.0 | 0 | The value is derived in accordance with the default allocation rule specified in the table above. | | 0.0 | > 0 | If**`_mb`**exceeds the`maximum_memory`, a value derived from the above table is used. Otherwise, the value of**`_mb`**is used as is. | | > 0.0 | Any value | The value of**`_percent`**is used. | If the `compiled_images_eviction_memory_limit_percent` variable is set to a value other than 0.0, the value of `compiled_images_eviction_memory_limit_mb` is ignored. > **📝 Note**: Changes to `maximum_memory` may result in changes in the module cache limit, in accordance with the rules specified above. ## Drop Plans from the Plancache In addition to setting a retention policy for in-memory and on-disk plans, you may also choose to drop plans from the plancache to either compile a new query plan or reduce memory usage. For running nodes, the following three commands can drop a plan from the plancache: [DROP … FROM PLANCACHE](https://docs.singlestore.com/cloud/reference/sql-reference/data-definition-language-ddl/drop-from-plancache.md) , [ALTER TABLE](https://docs.singlestore.com/cloud/reference/sql-reference/data-definition-language-ddl/alter-table.md), and [ANALYZE](https://docs.singlestore.com/cloud/reference/sql-reference/operational-commands/analyze.md). Successful completion of a new `ALTER TABLE` will invalidate the plancache for all queries that operate on the affected table, requiring their recompilation. The invalidation of the plancaches happens asynchronously. That is, new queries will compile and use new query plans, while currently running queries will use the old query plans. Once no queries are using the old query plans, they are marked as ready to be purged by the garbage collector. `ANALYZE` [invalidates stale plans](https://docs.singlestore.com/cloud/reference/sql-reference/operational-commands/analyze.md) from both the in-memory and the on-disk plancache, including plans which are on-disk but not in-memory. This invalidation ensures that all stale plans are discarded and that they are recompiled the next time the query is run. > **📝 Note**: The `ANALYZE` command invalidates plans by marking them as invalid so they won’t be used in the future, but it does not actually delete all the files in the on-disk plancache. The files will still be on disk, so it is not possible to reduce disk usage of the on-disk plancache with this command. ## Drop All Plans from the Plancache To remove all plans from the in-memory and on-disk plancaches, SingleStore recommends the practice of temporarily setting `plan_expiration_minutes` and `disk_plan_expiration_minutes` to `0`. Setting these engine variables to `0` will cause the plans in the plancaches to be marked as invalid and subsequently deleted by the garbage collector. To forcibly drop all plans in the in-memory and on-disk plancaches: Run `SHOW VARIABLES` and save the current values for the plan expiration minutes engine variables. ```sql SHOW VARIABLES LIKE '%plan_expiration_minutes'; /* be sure to save these values */ ``` Set the plan expiration minutes engine variables to `0` and invoke `SLEEP` to give the garbage collector time to delete the plans. A larger value for `SLEEP` may be needed depending on the size of the plancache and the speed of your disks. ```sql SET GLOBAL plan_expiration_minutes=0; SET GLOBAL disk_plan_expiration_minutes=0; SELECT SLEEP(300); ``` Reset the plan expiration minutes engine variables to their previous values. ```sql SET GLOBAL plan_expiration_minutes=; SET GLOBAL disk_plan_expiration_minutes=; ``` ## Related Topics * [Code Generation](https://docs.singlestore.com/cloud/query-data/advanced-query-topics/code-generation.md) *** Modified at: March 25, 2026 Source: [/cloud/user-and-workspace-administration/workspace-health-and-performance/managing-plancache-memory-and-disk-usage/](https://docs.singlestore.com/cloud/user-and-workspace-administration/workspace-health-and-performance/managing-plancache-memory-and-disk-usage/) (An index of the documentation is available at /llms.txt)