Zabbix

/*

** Zabbix

** Copyright (C) 2001-2023 Zabbix SIA

**

** This program is free software; you can redistribute it and/or modify

** it under the terms of the GNU General Public License as published by

** the Free Software Foundation; either version 2 of the License, or

** (at your option) any later version.

**

** This program is distributed in the hope that it will be useful,

** but WITHOUT ANY WARRANTY; without even the implied warranty of

** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

** GNU General Public License for more details.

**

** You should have received a copy of the GNU General Public License

** along with this program; if not, write to the Free Software

** Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

**/

​

#include "zbxcachevalue.h"

​

#include "zbxmutexs.h"

#include "zbxtime.h"

#include "zbxvariant.h"

​

/*

 * The cache (zbx_vc_cache_t) is organized as a hashset of item records (zbx_vc_item_t).

 *

 * Each record holds item data (itemid, value_type), statistics (hits, last access time,...)

 * and the historical data (timestamp,value pairs in ascending order).

 *

 * The historical data are stored from largest request (+timeshift) range to the

 * current time. The data is automatically fetched from DB whenever a request

 * exceeds cached value range.

 *

 * In addition to active range value cache tracks item range for last 24 hours. Once

 * per day the active range is updated with daily range and the daily range is reset.

 *

 * If an item is already being cached the new values are automatically added to the cache

 * after being written into database.

 *

 * When cache runs out of memory to store new items it enters in low memory mode.

 * In low memory mode cache continues to function as before with few restrictions:

 *   1) items that weren't accessed during the last day are removed from cache.

 *   2) items with worst hits/values ratio might be removed from cache to free the space.

 *   3) no new items are added to the cache.

 *

 * The low memory mode can't be turned off - it will persist until server is rebooted.

 * In low memory mode a warning message is written into log every 5 minutes.

 */

​

/* the period of low memory warning messages */

#define ZBX_VC_LOW_MEMORY_WARNING_PERIOD    (5 * SEC_PER_MIN)

​

/* time period after which value cache will switch back to normal mode */

#define ZBX_VC_LOW_MEMORY_RESET_PERIOD      SEC_PER_DAY

​

#define ZBX_VC_LOW_MEMORY_ITEM_PRINT_LIMIT  25

​

static zbx_shmem_info_t *vc_mem = NULL;

​

zbx_rwlock_t    vc_lock = ZBX_RWLOCK_NULL;

​

/* value cache enable/disable flags */

#define ZBX_VC_DISABLED     0

#define ZBX_VC_ENABLED      1

​

/* value cache state, after initialization value cache is always disabled */

static int  vc_state = ZBX_VC_DISABLED;

​

ZBX_SHMEM_FUNC_IMPL(__vc, vc_mem)

​

#define VC_STRPOOL_INIT_SIZE    (1000)

#define VC_ITEMS_INIT_SIZE  (1000)

​

#define VC_MAX_NANOSECONDS  999999999

​

#define VC_MIN_RANGE            SEC_PER_MIN

​

/* the range synchronization period in hours */

#define ZBX_VC_RANGE_SYNC_PERIOD    24

​

#define ZBX_VC_ITEM_EXPIRE_PERIOD   SEC_PER_DAY

​

/* the data chunk used to store data fragment */

typedef struct zbx_vc_chunk

{

    /* a pointer to the previous chunk or NULL if this is the tail chunk */

    struct zbx_vc_chunk *prev;

​

    /* a pointer to the next chunk or NULL if this is the head chunk */