path: root/src/third_party/wiredtiger/src/include/session.h

/*-
 * Copyright (c) 2014-2019 MongoDB, Inc.
 * Copyright (c) 2008-2014 WiredTiger, Inc.
 *	All rights reserved.
 *
 * See the file LICENSE for redistribution information.
 */

/*
 * WT_DATA_HANDLE_CACHE --
 *	Per-session cache of handles to avoid synchronization when opening
 *	cursors.
 */
struct __wt_data_handle_cache {
    WT_DATA_HANDLE *dhandle;

    TAILQ_ENTRY(__wt_data_handle_cache) q;
    TAILQ_ENTRY(__wt_data_handle_cache) hashq;
};

/*
 * WT_HAZARD --
 *	A hazard pointer.
 */
struct __wt_hazard {
    WT_REF *ref; /* Page reference */
#ifdef HAVE_DIAGNOSTIC
    const char *func; /* Function/line hazard acquired */
    int line;
#endif
};

/* Get the connection implementation for a session */
#define S2C(session) ((WT_CONNECTION_IMPL *)(session)->iface.connection)

/* Get the btree for a session */
#define S2BT(session) ((WT_BTREE *)(session)->dhandle->handle)
#define S2BT_SAFE(session) ((session)->dhandle == NULL ? NULL : S2BT(session))

typedef TAILQ_HEAD(__wt_cursor_list, __wt_cursor) WT_CURSOR_LIST;

/* Number of cursors cached to trigger cursor sweep. */
#define WT_SESSION_CURSOR_SWEEP_COUNTDOWN 40

/* Minimum number of buckets to visit during cursor sweep. */
#define WT_SESSION_CURSOR_SWEEP_MIN 5

/* Maximum number of buckets to visit during cursor sweep. */
#define WT_SESSION_CURSOR_SWEEP_MAX 32
/*
 * WT_SESSION_IMPL --
 *	Implementation of WT_SESSION.
 */
struct __wt_session_impl {
    WT_SESSION iface;

    void *lang_private; /* Language specific private storage */

    u_int active; /* Non-zero if the session is in-use */

    const char *name;   /* Name */
    const char *lastop; /* Last operation */
    uint32_t id;        /* UID, offset in session array */

    uint64_t operation_start_us;   /* Operation start */
    uint64_t operation_timeout_us; /* Maximum operation period before rollback */
#ifdef HAVE_DIAGNOSTIC
    uint32_t op_5043_seconds; /* Temporary debugging to catch WT-5043, discard after 01/2020. */
#endif

    WT_EVENT_HANDLER *event_handler; /* Application's event handlers */

    WT_DATA_HANDLE *dhandle; /* Current data handle */

    /*
     * Each session keeps a cache of data handles. The set of handles can grow quite large so we
     * maintain both a simple list and a hash table of lists. The hash table key is based on a hash
     * of the data handle's URI. The hash table list is kept in allocated memory that lives across
     * session close - so it is declared further down.
     */
    /* Session handle reference list */
    TAILQ_HEAD(__dhandles, __wt_data_handle_cache) dhandles;
    uint64_t last_sweep;        /* Last sweep for dead handles */
    struct timespec last_epoch; /* Last epoch time returned */

    WT_CURSOR_LIST cursors;          /* Cursors closed with the session */
    uint32_t cursor_sweep_position;  /* Position in cursor_cache for sweep */
    uint32_t cursor_sweep_countdown; /* Countdown to cursor sweep */
    uint64_t last_cursor_sweep;      /* Last sweep for dead cursors */

    WT_CURSOR_BACKUP *bkp_cursor; /* Hot backup cursor */

    WT_COMPACT_STATE *compact; /* Compaction information */
    enum { WT_COMPACT_NONE = 0, WT_COMPACT_RUNNING, WT_COMPACT_SUCCESS } compact_state;

    WT_CURSOR *las_cursor; /* Lookaside table cursor */

    WT_CURSOR *meta_cursor;  /* Metadata file */
    void *meta_track;        /* Metadata operation tracking */
    void *meta_track_next;   /* Current position */
    void *meta_track_sub;    /* Child transaction / save point */
    size_t meta_track_alloc; /* Currently allocated */
    int meta_track_nest;     /* Nesting level of meta transaction */
#define WT_META_TRACKING(session) ((session)->meta_track_next != NULL)

    /* Current rwlock for callback. */
    WT_RWLOCK *current_rwlock;
    uint8_t current_rwticket;

    WT_ITEM **scratch;     /* Temporary memory for any function */
    u_int scratch_alloc;   /* Currently allocated */
    size_t scratch_cached; /* Scratch bytes cached */
#ifdef HAVE_DIAGNOSTIC
    /*
     * Variables used to look for violations of the contract that a session is only used by a single
     * session at once.
     */
    volatile uintmax_t api_tid;
    volatile uint32_t api_enter_refcnt;
    /*
     * It's hard to figure out from where a buffer was allocated after it's leaked, so in diagnostic
     * mode we track them; DIAGNOSTIC can't simply add additional fields to WT_ITEM structures
     * because they are visible to applications, create a parallel structure instead.
     */
    struct __wt_scratch_track {
        const char *func; /* Allocating function, line */
        int line;
    } * scratch_track;
#endif

    WT_ITEM err; /* Error buffer */

    WT_TXN_ISOLATION isolation;
    WT_TXN txn; /* Transaction state */
#define WT_SESSION_BG_SYNC_MSEC 1200000
    WT_LSN bg_sync_lsn; /* Background sync operation LSN. */
    u_int ncursors;     /* Count of active file cursors. */

    void *block_manager; /* Block-manager support */
    int (*block_manager_cleanup)(WT_SESSION_IMPL *);

    /* Checkpoint handles */
    WT_DATA_HANDLE **ckpt_handle; /* Handle list */
    u_int ckpt_handle_next;       /* Next empty slot */
    size_t ckpt_handle_allocated; /* Bytes allocated */

    uint64_t cache_wait_us; /* Wait time for cache for current operation */

    /*
     * Operations acting on handles.
     *
     * The preferred pattern is to gather all of the required handles at
     * the beginning of an operation, then drop any other locks, perform
     * the operation, then release the handles.  This cannot be easily
     * merged with the list of checkpoint handles because some operations
     * (such as compact) do checkpoints internally.
     */
    WT_DATA_HANDLE **op_handle; /* Handle list */
    u_int op_handle_next;       /* Next empty slot */
    size_t op_handle_allocated; /* Bytes allocated */

    void *reconcile; /* Reconciliation support */
    int (*reconcile_cleanup)(WT_SESSION_IMPL *);

    /* Sessions have an associated statistics bucket based on its ID. */
    u_int stat_bucket; /* Statistics bucket offset */

/* AUTOMATIC FLAG VALUE GENERATION START */
#define WT_SESSION_BACKUP_CURSOR 0x00000001u
#define WT_SESSION_BACKUP_DUP 0x00000002u
#define WT_SESSION_CACHE_CURSORS 0x00000004u
#define WT_SESSION_CAN_WAIT 0x00000008u
#define WT_SESSION_IGNORE_CACHE_SIZE 0x00000010u
#define WT_SESSION_INTERNAL 0x00000020u
#define WT_SESSION_LOCKED_CHECKPOINT 0x00000040u
#define WT_SESSION_LOCKED_HANDLE_LIST_READ 0x00000080u
#define WT_SESSION_LOCKED_HANDLE_LIST_WRITE 0x00000100u
#define WT_SESSION_LOCKED_HOTBACKUP_READ 0x00000200u
#define WT_SESSION_LOCKED_HOTBACKUP_WRITE 0x00000400u
#define WT_SESSION_LOCKED_METADATA 0x00000800u
#define WT_SESSION_LOCKED_PASS 0x00001000u
#define WT_SESSION_LOCKED_SCHEMA 0x00002000u
#define WT_SESSION_LOCKED_SLOT 0x00004000u
#define WT_SESSION_LOCKED_TABLE_READ 0x00008000u
#define WT_SESSION_LOCKED_TABLE_WRITE 0x00010000u
#define WT_SESSION_LOCKED_TURTLE 0x00020000u
#define WT_SESSION_LOGGING_INMEM 0x00040000u
#define WT_SESSION_LOOKASIDE_CURSOR 0x00080000u
#define WT_SESSION_NO_DATA_HANDLES 0x00100000u
#define WT_SESSION_NO_LOGGING 0x00200000u
#define WT_SESSION_NO_RECONCILE 0x00400000u
#define WT_SESSION_NO_SCHEMA_LOCK 0x00800000u
#define WT_SESSION_QUIET_CORRUPT_FILE 0x01000000u
#define WT_SESSION_READ_WONT_NEED 0x02000000u
#define WT_SESSION_RESOLVING_TXN 0x04000000u
#define WT_SESSION_SCHEMA_TXN 0x08000000u
#define WT_SESSION_SERVER_ASYNC 0x10000000u
    /* AUTOMATIC FLAG VALUE GENERATION STOP */
    uint32_t flags;

/*
 * All of the following fields live at the end of the structure so it's easier to clear everything
 * but the fields that persist.
 */
#define WT_SESSION_CLEAR_SIZE (offsetof(WT_SESSION_IMPL, rnd))

    /*
     * The random number state persists past session close because we don't want to repeatedly use
     * the same values for skiplist depth when the application isn't caching sessions.
     */
    WT_RAND_STATE rnd; /* Random number generation state */

    /*
     * Hash tables are allocated lazily as sessions are used to keep the size of this structure from
     * growing too large.
     */
    WT_CURSOR_LIST *cursor_cache; /* Hash table of cached cursors */

    /* Hashed handle reference list array */
    TAILQ_HEAD(__dhandles_hash, __wt_data_handle_cache) * dhhash;

/* Generations manager */
#define WT_GEN_CHECKPOINT 0 /* Checkpoint generation */
#define WT_GEN_COMMIT 1     /* Commit generation */
#define WT_GEN_EVICT 2      /* Eviction generation */
#define WT_GEN_HAZARD 3     /* Hazard pointer */
#define WT_GEN_SPLIT 4      /* Page splits */
#define WT_GENERATIONS 5    /* Total generation manager entries */
    volatile uint64_t generations[WT_GENERATIONS];

    /*
     * Session memory persists past session close because it's accessed by threads of control other
     * than the thread owning the session. For example, btree splits and hazard pointers can "free"
     * memory that's still in use. In order to eventually free it, it's stashed here with its
     * generation number; when no thread is reading in generation, the memory can be freed for real.
     */
    struct __wt_session_stash {
        struct __wt_stash {
            void *p; /* Memory, length */
            size_t len;
            uint64_t gen; /* Generation */
        } * list;
        size_t cnt;   /* Array entries */
        size_t alloc; /* Allocated bytes */
    } stash[WT_GENERATIONS];

/*
 * Hazard pointers.
 *
 * Hazard information persists past session close because it's accessed by threads of control other
 * than the thread owning the session.
 *
 * Use the non-NULL state of the hazard field to know if the session has previously been
 * initialized.
 */
#define WT_SESSION_FIRST_USE(s) ((s)->hazard == NULL)

/*
 * The hazard pointer array grows as necessary, initialize with 250 slots.
 */
#define WT_SESSION_INITIAL_HAZARD_SLOTS 250
    uint32_t hazard_size;  /* Hazard pointer array slots */
    uint32_t hazard_inuse; /* Hazard pointer array slots in-use */
    uint32_t nhazard;      /* Count of active hazard pointers */
    WT_HAZARD *hazard;     /* Hazard pointer array */

    /*
     * Operation tracking.
     */
    WT_OPTRACK_RECORD *optrack_buf;
    u_int optrackbuf_ptr;
    uint64_t optrack_offset;
    WT_FH *optrack_fh;

    WT_SESSION_STATS stats;
};