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/*-
* Copyright (c) 2014-2016 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#define WT_TXN_NONE 0 /* No txn running in a session. */
#define WT_TXN_FIRST 1 /* First transaction to run. */
#define WT_TXN_ABORTED UINT64_MAX /* Update rolled back, ignore. */
/*
* Transaction ID comparison dealing with edge cases.
*
* WT_TXN_ABORTED is the largest possible ID (never visible to a running
* transaction), WT_TXN_NONE is smaller than any possible ID (visible to all
* running transactions).
*/
#define WT_TXNID_LE(t1, t2) \
((t1) <= (t2))
#define WT_TXNID_LT(t1, t2) \
((t1) < (t2))
#define WT_SESSION_TXN_STATE(s) (&S2C(s)->txn_global.states[(s)->id])
#define WT_SESSION_IS_CHECKPOINT(s) \
((s)->id != 0 && (s)->id == S2C(s)->txn_global.checkpoint_id)
/*
* Perform an operation at the specified isolation level.
*
* This is fiddly: we can't cope with operations that begin transactions
* (leaving an ID allocated), and operations must not move our published
* snap_min forwards (or updates we need could be freed while this operation is
* in progress). Check for those cases: the bugs they cause are hard to debug.
*/
#define WT_WITH_TXN_ISOLATION(s, iso, op) do { \
WT_TXN_ISOLATION saved_iso = (s)->isolation; \
WT_TXN_ISOLATION saved_txn_iso = (s)->txn.isolation; \
WT_TXN_STATE *txn_state = WT_SESSION_TXN_STATE(s); \
WT_TXN_STATE saved_state = *txn_state; \
(s)->txn.forced_iso++; \
(s)->isolation = (s)->txn.isolation = (iso); \
op; \
(s)->isolation = saved_iso; \
(s)->txn.isolation = saved_txn_iso; \
WT_ASSERT((s), (s)->txn.forced_iso > 0); \
(s)->txn.forced_iso--; \
WT_ASSERT((s), txn_state->id == saved_state.id && \
(txn_state->metadata_pinned == saved_state.metadata_pinned ||\
saved_state.metadata_pinned == WT_TXN_NONE) && \
(txn_state->pinned_id == saved_state.pinned_id || \
saved_state.pinned_id == WT_TXN_NONE)); \
txn_state->metadata_pinned = saved_state.metadata_pinned; \
txn_state->pinned_id = saved_state.pinned_id; \
} while (0)
struct __wt_named_snapshot {
const char *name;
TAILQ_ENTRY(__wt_named_snapshot) q;
uint64_t id, pinned_id, snap_min, snap_max;
uint64_t *snapshot;
uint32_t snapshot_count;
};
struct __wt_txn_state {
WT_CACHE_LINE_PAD_BEGIN
volatile uint64_t id;
volatile uint64_t pinned_id;
volatile uint64_t metadata_pinned;
WT_CACHE_LINE_PAD_END
};
struct __wt_txn_global {
WT_SPINLOCK id_lock;
volatile uint64_t current; /* Current transaction ID. */
/* The oldest running transaction ID (may race). */
volatile uint64_t last_running;
/*
* The oldest transaction ID that is not yet visible to some
* transaction in the system.
*/
volatile uint64_t oldest_id;
/*
* Prevents the oldest ID moving forwards while threads are scanning
* the global transaction state.
*/
WT_RWLOCK *scan_rwlock;
/*
* Track information about the running checkpoint. The transaction
* snapshot used when checkpointing are special. Checkpoints can run
* for a long time so we keep them out of regular visibility checks.
* Eviction and checkpoint operations know when they need to be aware
* of checkpoint transactions.
*
* We rely on the fact that (a) the only table a checkpoint updates is
* the metadata; and (b) once checkpoint has finished reading a table,
* it won't revisit it.
*/
volatile bool checkpoint_running; /* Checkpoint running */
volatile uint32_t checkpoint_id; /* Checkpoint's session ID */
volatile uint64_t checkpoint_gen; /* Checkpoint generation */
volatile uint64_t checkpoint_pinned; /* Oldest ID for checkpoint */
volatile uint64_t checkpoint_txnid; /* Checkpoint's txn ID */
volatile uint64_t metadata_pinned; /* Oldest ID for metadata */
/* Named snapshot state. */
WT_RWLOCK *nsnap_rwlock;
volatile uint64_t nsnap_oldest_id;
TAILQ_HEAD(__wt_nsnap_qh, __wt_named_snapshot) nsnaph;
WT_TXN_STATE *states; /* Per-session transaction states */
};
typedef enum __wt_txn_isolation {
WT_ISO_READ_COMMITTED,
WT_ISO_READ_UNCOMMITTED,
WT_ISO_SNAPSHOT
} WT_TXN_ISOLATION;
/*
* WT_TXN_OP --
* A transactional operation. Each transaction builds an in-memory array
* of these operations as it runs, then uses the array to either write log
* records during commit or undo the operations during rollback.
*/
struct __wt_txn_op {
uint32_t fileid;
enum {
WT_TXN_OP_BASIC,
WT_TXN_OP_INMEM,
WT_TXN_OP_REF,
WT_TXN_OP_TRUNCATE_COL,
WT_TXN_OP_TRUNCATE_ROW
} type;
union {
/* WT_TXN_OP_BASIC, WT_TXN_OP_INMEM */
WT_UPDATE *upd;
/* WT_TXN_OP_REF */
WT_REF *ref;
/* WT_TXN_OP_TRUNCATE_COL */
struct {
uint64_t start, stop;
} truncate_col;
/* WT_TXN_OP_TRUNCATE_ROW */
struct {
WT_ITEM start, stop;
enum {
WT_TXN_TRUNC_ALL,
WT_TXN_TRUNC_BOTH,
WT_TXN_TRUNC_START,
WT_TXN_TRUNC_STOP
} mode;
} truncate_row;
} u;
};
/*
* WT_TXN --
* Per-session transaction context.
*/
struct __wt_txn {
uint64_t id;
WT_TXN_ISOLATION isolation;
uint32_t forced_iso; /* Isolation is currently forced. */
/*
* Snapshot data:
* ids < snap_min are visible,
* ids > snap_max are invisible,
* everything else is visible unless it is in the snapshot.
*/
uint64_t snap_min, snap_max;
uint64_t *snapshot;
uint32_t snapshot_count;
uint32_t txn_logsync; /* Log sync configuration */
/* Array of modifications by this transaction. */
WT_TXN_OP *mod;
size_t mod_alloc;
u_int mod_count;
/* Scratch buffer for in-memory log records. */
WT_ITEM *logrec;
/* Requested notification when transactions are resolved. */
WT_TXN_NOTIFY *notify;
/* Checkpoint status. */
WT_LSN ckpt_lsn;
uint32_t ckpt_nsnapshot;
WT_ITEM *ckpt_snapshot;
bool full_ckpt;
#define WT_TXN_AUTOCOMMIT 0x01
#define WT_TXN_ERROR 0x02
#define WT_TXN_HAS_ID 0x04
#define WT_TXN_HAS_SNAPSHOT 0x08
#define WT_TXN_NAMED_SNAPSHOT 0x10
#define WT_TXN_READONLY 0x20
#define WT_TXN_RUNNING 0x40
#define WT_TXN_SYNC_SET 0x80
uint32_t flags;
};
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