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diff --git a/include/zbxcachevalue.h b/include/zbxcachevalue.h
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+/*
+** Zabbix
+** Copyright (C) 2001-2022 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.
+**/
+
+#ifndef ZABBIX_CACHEVALUE_H
+#define ZABBIX_CACHEVALUE_H
+
+#include "zbxtypes.h"
+#include "zbxalgo.h"
+#include "zbxhistory.h"
+#include "zbxshmem.h"
+
+/*
+ * The Value Cache provides read caching of item historical data residing in history
+ * tables. No components must read history tables manually. Instead all history data
+ * must be read from the Value Cache.
+ *
+ * Usage notes:
+ *
+ * Initialization
+ *
+ *   The value cache must be initialized at the start of the program with zbx_vc_init()
+ *   function. To ensure proper removal of shared memory the value cache must be destroyed
+ *   upon a program exit with zbx_vc_destroy() function.
+ *
+ * Adding data
+ *
+ *   Whenever a new item value is added to system (history tables) the item value must be
+ *   also added added to Value Cache with zbx_dc_add_value() function to keep it up to date.
+ *
+ * Retrieving data
+ *
+ *   The history data is accessed with zbx_vc_get_values() and zbx_vc_get_value()
+ *   functions. Afterwards the retrieved history data must be freed by the caller by using
+ *   either zbx_history_record_vector_destroy() function (free the zbx_vc_get_values()
+ *   call output) or zbx_history_record_clear() function (free the zbx_vc_get_value() call output).
+ *
+ * Locking
+ *
+ *   The cache ensures synchronization between processes by using automatic locks whenever
+ *   a cache function (zbx_vc_*) is called and by providing manual cache locking functionality
+ *   with zbx_vc_lock()/zbx_vc_unlock() functions.
+ *
+ */
+
+#define ZBX_VC_MODE_NORMAL	0
+#define ZBX_VC_MODE_LOWMEM	1
+
+/* indicates that all values from database are cached */
+#define ZBX_ITEM_STATUS_CACHED_ALL	1
+
+/* the cache statistics */
+typedef struct
+{
+	/* Value cache misses are new values cached during request and hits are calculated by  */
+	/* subtracting misses from the total number of values returned (0 if the number of     */
+	/* returned values is less than misses.                                                */
+	/* When performing count based requests the number of cached values might be greater   */
+	/* than number of returned values. This can skew the hits/misses ratio towards misses. */
+	zbx_uint64_t	hits;
+	zbx_uint64_t	misses;
+
+	zbx_uint64_t	total_size;
+	zbx_uint64_t	free_size;
+
+	/* value cache operating mode - see ZBX_VC_MODE_* defines */
+	int		mode;
+}
+zbx_vc_stats_t;
+
+/* item diagnostic statistics */
+typedef struct
+{
+	zbx_uint64_t	itemid;
+	int		values_num;
+	int		hourly_num;
+}
+zbx_vc_item_stats_t;
+
+int	zbx_vc_init(char **error);
+
+void	zbx_vc_destroy(void);
+
+void	zbx_vc_reset(void);
+
+void	zbx_vc_enable(void);
+
+void	zbx_vc_disable(void);
+
+int	zbx_vc_get_values(zbx_uint64_t itemid, unsigned char value_type, zbx_vector_history_record_t *values,
+		int seconds, int count, const zbx_timespec_t *ts);
+
+int	zbx_vc_get_value(zbx_uint64_t itemid, unsigned char value_type, const zbx_timespec_t *ts,
+		zbx_history_record_t *value);
+
+int	zbx_vc_add_values(zbx_vector_ptr_t *history, int *ret_flush);
+
+int	zbx_vc_get_statistics(zbx_vc_stats_t *stats);
+
+void	zbx_vc_remove_items_by_ids(zbx_vector_uint64_t *itemids);
+
+void	zbx_vc_get_diag_stats(zbx_uint64_t *items_num, zbx_uint64_t *values_num, int *mode);
+void	zbx_vc_get_mem_stats(zbx_shmem_stats_t *mem);
+void	zbx_vc_get_item_stats(zbx_vector_ptr_t *stats);
+void	zbx_vc_flush_stats(void);
+
+#endif