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/* ----------
* pgstat_internal.h
*
* Definitions for the PostgreSQL cumulative statistics system that should
* only be needed by files implementing statistics support (rather than ones
* reporting / querying stats).
*
* Copyright (c) 2001-2023, PostgreSQL Global Development Group
*
* src/include/utils/pgstat_internal.h
* ----------
*/
#ifndef PGSTAT_INTERNAL_H
#define PGSTAT_INTERNAL_H
#include "common/hashfn.h"
#include "lib/dshash.h"
#include "lib/ilist.h"
#include "pgstat.h"
#include "storage/lwlock.h"
#include "utils/dsa.h"
/*
* Types related to shared memory storage of statistics.
*
* Per-object statistics are stored in the "shared stats" hashtable. That
* table's entries (PgStatShared_HashEntry) contain a pointer to the actual stats
* data for the object (the size of the stats data varies depending on the
* kind of stats). The table is keyed by PgStat_HashKey.
*
* Once a backend has a reference to a shared stats entry, it increments the
* entry's refcount. Even after stats data is dropped (e.g., due to a DROP
* TABLE), the entry itself can only be deleted once all references have been
* released.
*
* These refcounts, in combination with a backend local hashtable
* (pgStatEntryRefHash, with entries pointing to PgStat_EntryRef) in front of
* the shared hash table, mean that most stats work can happen without
* touching the shared hash table, reducing contention.
*
* Once there are pending stats updates for a table PgStat_EntryRef->pending
* is allocated to contain a working space for as-of-yet-unapplied stats
* updates. Once the stats are flushed, PgStat_EntryRef->pending is freed.
*
* Each stat kind in the shared hash table has a fixed member
* PgStatShared_Common as the first element.
*/
/* struct for shared statistics hash entry key. */
typedef struct PgStat_HashKey
{
PgStat_Kind kind; /* statistics entry kind */
Oid dboid; /* database ID. InvalidOid for shared objects. */
Oid objoid; /* object ID, either table or function. */
} PgStat_HashKey;
/*
* Shared statistics hash entry. Doesn't itself contain any stats, but points
* to them (with ->body). That allows the stats entries themselves to be of
* variable size.
*/
typedef struct PgStatShared_HashEntry
{
PgStat_HashKey key; /* hash key */
/*
* If dropped is set, backends need to release their references so that
* the memory for the entry can be freed. No new references may be made
* once marked as dropped.
*/
bool dropped;
/*
* Refcount managing lifetime of the entry itself (as opposed to the
* dshash entry pointing to it). The stats lifetime has to be separate
* from the hash table entry lifetime because we allow backends to point
* to a stats entry without holding a hash table lock (and some other
* reasons).
*
* As long as the entry is not dropped, 1 is added to the refcount
* representing that the entry should not be dropped. In addition each
* backend that has a reference to the entry needs to increment the
* refcount as long as it does.
*
* May only be incremented / decremented while holding at least a shared
* lock on the dshash partition containing the entry. It needs to be an
* atomic variable because multiple backends can increment the refcount
* with just a shared lock.
*
* When the refcount reaches 0 the entry needs to be freed.
*/
pg_atomic_uint32 refcount;
/*
* Pointer to shared stats. The stats entry always starts with
* PgStatShared_Common, embedded in a larger struct containing the
* PgStat_Kind specific stats fields.
*/
dsa_pointer body;
} PgStatShared_HashEntry;
/*
* Common header struct for PgStatShared_*.
*/
typedef struct PgStatShared_Common
{
uint32 magic; /* just a validity cross-check */
/* lock protecting stats contents (i.e. data following the header) */
LWLock lock;
} PgStatShared_Common;
/*
* A backend local reference to a shared stats entry. As long as at least one
* such reference exists, the shared stats entry will not be released.
*
* If there are pending stats update to the shared stats, these are stored in
* ->pending.
*/
typedef struct PgStat_EntryRef
{
/*
* Pointer to the PgStatShared_HashEntry entry in the shared stats
* hashtable.
*/
PgStatShared_HashEntry *shared_entry;
/*
* Pointer to the stats data (i.e. PgStatShared_HashEntry->body), resolved
* as a local pointer, to avoid repeated dsa_get_address() calls.
*/
PgStatShared_Common *shared_stats;
/*
* Pending statistics data that will need to be flushed to shared memory
* stats eventually. Each stats kind utilizing pending data defines what
* format its pending data has and needs to provide a
* PgStat_KindInfo->flush_pending_cb callback to merge pending into shared
* stats.
*/
void *pending;
dlist_node pending_node; /* membership in pgStatPending list */
} PgStat_EntryRef;
/*
* Some stats changes are transactional. To maintain those, a stack of
* PgStat_SubXactStatus entries is maintained, which contain data pertaining
* to the current transaction and its active subtransactions.
*/
typedef struct PgStat_SubXactStatus
{
int nest_level; /* subtransaction nest level */
struct PgStat_SubXactStatus *prev; /* higher-level subxact if any */
/*
* Statistics for transactionally dropped objects need to be
* transactionally dropped as well. Collect the stats dropped in the
* current (sub-)transaction and only execute the stats drop when we know
* if the transaction commits/aborts. To handle replicas and crashes,
* stats drops are included in commit / abort records.
*/
dclist_head pending_drops;
/*
* Tuple insertion/deletion counts for an open transaction can't be
* propagated into PgStat_TableStatus counters until we know if it is
* going to commit or abort. Hence, we keep these counts in per-subxact
* structs that live in TopTransactionContext. This data structure is
* designed on the assumption that subxacts won't usually modify very many
* tables.
*/
PgStat_TableXactStatus *first; /* head of list for this subxact */
} PgStat_SubXactStatus;
/*
* Metadata for a specific kind of statistics.
*/
typedef struct PgStat_KindInfo
{
/*
* Do a fixed number of stats objects exist for this kind of stats (e.g.
* bgwriter stats) or not (e.g. tables).
*/
bool fixed_amount:1;
/*
* Can stats of this kind be accessed from another database? Determines
* whether a stats object gets included in stats snapshots.
*/
bool accessed_across_databases:1;
/*
* For variable-numbered stats: Identified on-disk using a name, rather
* than PgStat_HashKey. Probably only needed for replication slot stats.
*/
bool named_on_disk:1;
/*
* The size of an entry in the shared stats hash table (pointed to by
* PgStatShared_HashEntry->body).
*/
uint32 shared_size;
/*
* The offset/size of statistics inside the shared stats entry. Used when
* [de-]serializing statistics to / from disk respectively. Separate from
* shared_size because [de-]serialization may not include in-memory state
* like lwlocks.
*/
uint32 shared_data_off;
uint32 shared_data_len;
/*
* The size of the pending data for this kind. E.g. how large
* PgStat_EntryRef->pending is. Used for allocations.
*
* 0 signals that an entry of this kind should never have a pending entry.
*/
uint32 pending_size;
/*
* For variable-numbered stats: flush pending stats. Required if pending
* data is used.
*/
bool (*flush_pending_cb) (PgStat_EntryRef *sr, bool nowait);
/*
* For variable-numbered stats: delete pending stats. Optional.
*/
void (*delete_pending_cb) (PgStat_EntryRef *sr);
/*
* For variable-numbered stats: reset the reset timestamp. Optional.
*/
void (*reset_timestamp_cb) (PgStatShared_Common *header, TimestampTz ts);
/*
* For variable-numbered stats with named_on_disk. Optional.
*/
void (*to_serialized_name) (const PgStat_HashKey *key,
const PgStatShared_Common *header, NameData *name);
bool (*from_serialized_name) (const NameData *name, PgStat_HashKey *key);
/*
* For fixed-numbered statistics: Reset All.
*/
void (*reset_all_cb) (TimestampTz ts);
/*
* For fixed-numbered statistics: Build snapshot for entry
*/
void (*snapshot_cb) (void);
/* name of the kind of stats */
const char *const name;
} PgStat_KindInfo;
/*
* List of SLRU names that we keep stats for. There is no central registry of
* SLRUs, so we use this fixed list instead. The "other" entry is used for
* all SLRUs without an explicit entry (e.g. SLRUs in extensions).
*
* This is only defined here so that SLRU_NUM_ELEMENTS is known for later type
* definitions.
*/
static const char *const slru_names[] = {
"CommitTs",
"MultiXactMember",
"MultiXactOffset",
"Notify",
"Serial",
"Subtrans",
"Xact",
"other" /* has to be last */
};
#define SLRU_NUM_ELEMENTS lengthof(slru_names)
/* ----------
* Types and definitions for different kinds of fixed-amount stats.
*
* Single-writer stats use the changecount mechanism to achieve low-overhead
* writes - they're obviously more performance critical than reads. Check the
* definition of struct PgBackendStatus for some explanation of the
* changecount mechanism.
*
* Because the obvious implementation of resetting single-writer stats isn't
* compatible with that (another backend needs to write), we don't scribble on
* shared stats while resetting. Instead, just record the current counter
* values in a copy of the stats data, which is protected by ->lock. See
* pgstat_fetch_stat_(archiver|bgwriter|checkpointer) for the reader side.
*
* The only exception to that is the stat_reset_timestamp in these structs,
* which is protected by ->lock, because it has to be written by another
* backend while resetting.
* ----------
*/
typedef struct PgStatShared_Archiver
{
/* lock protects ->reset_offset as well as stats->stat_reset_timestamp */
LWLock lock;
uint32 changecount;
PgStat_ArchiverStats stats;
PgStat_ArchiverStats reset_offset;
} PgStatShared_Archiver;
typedef struct PgStatShared_BgWriter
{
/* lock protects ->reset_offset as well as stats->stat_reset_timestamp */
LWLock lock;
uint32 changecount;
PgStat_BgWriterStats stats;
PgStat_BgWriterStats reset_offset;
} PgStatShared_BgWriter;
typedef struct PgStatShared_Checkpointer
{
/* lock protects ->reset_offset as well as stats->stat_reset_timestamp */
LWLock lock;
uint32 changecount;
PgStat_CheckpointerStats stats;
PgStat_CheckpointerStats reset_offset;
} PgStatShared_Checkpointer;
/* Shared-memory ready PgStat_IO */
typedef struct PgStatShared_IO
{
/*
* locks[i] protects stats.stats[i]. locks[0] also protects
* stats.stat_reset_timestamp.
*/
LWLock locks[BACKEND_NUM_TYPES];
PgStat_IO stats;
} PgStatShared_IO;
typedef struct PgStatShared_SLRU
{
/* lock protects ->stats */
LWLock lock;
PgStat_SLRUStats stats[SLRU_NUM_ELEMENTS];
} PgStatShared_SLRU;
typedef struct PgStatShared_Wal
{
/* lock protects ->stats */
LWLock lock;
PgStat_WalStats stats;
} PgStatShared_Wal;
/* ----------
* Types and definitions for different kinds of variable-amount stats.
*
* Each struct has to start with PgStatShared_Common, containing information
* common across the different types of stats. Kind-specific data follows.
* ----------
*/
typedef struct PgStatShared_Database
{
PgStatShared_Common header;
PgStat_StatDBEntry stats;
} PgStatShared_Database;
typedef struct PgStatShared_Relation
{
PgStatShared_Common header;
PgStat_StatTabEntry stats;
} PgStatShared_Relation;
typedef struct PgStatShared_Function
{
PgStatShared_Common header;
PgStat_StatFuncEntry stats;
} PgStatShared_Function;
typedef struct PgStatShared_Subscription
{
PgStatShared_Common header;
PgStat_StatSubEntry stats;
} PgStatShared_Subscription;
typedef struct PgStatShared_ReplSlot
{
PgStatShared_Common header;
PgStat_StatReplSlotEntry stats;
} PgStatShared_ReplSlot;
/*
* Central shared memory entry for the cumulative stats system.
*
* Fixed amount stats, the dynamic shared memory hash table for
* non-fixed-amount stats, as well as remaining bits and pieces are all
* reached from here.
*/
typedef struct PgStat_ShmemControl
{
void *raw_dsa_area;
/*
* Stats for variable-numbered objects are kept in this shared hash table.
* See comment above PgStat_Kind for details.
*/
dshash_table_handle hash_handle; /* shared dbstat hash */
/* Has the stats system already been shut down? Just a debugging check. */
bool is_shutdown;
/*
* Whenever statistics for dropped objects could not be freed - because
* backends still have references - the dropping backend calls
* pgstat_request_entry_refs_gc() incrementing this counter. Eventually
* that causes backends to run pgstat_gc_entry_refs(), allowing memory to
* be reclaimed.
*/
pg_atomic_uint64 gc_request_count;
/*
* Stats data for fixed-numbered objects.
*/
PgStatShared_Archiver archiver;
PgStatShared_BgWriter bgwriter;
PgStatShared_Checkpointer checkpointer;
PgStatShared_IO io;
PgStatShared_SLRU slru;
PgStatShared_Wal wal;
} PgStat_ShmemControl;
/*
* Cached statistics snapshot
*/
typedef struct PgStat_Snapshot
{
PgStat_FetchConsistency mode;
/* time at which snapshot was taken */
TimestampTz snapshot_timestamp;
bool fixed_valid[PGSTAT_NUM_KINDS];
PgStat_ArchiverStats archiver;
PgStat_BgWriterStats bgwriter;
PgStat_CheckpointerStats checkpointer;
PgStat_IO io;
PgStat_SLRUStats slru[SLRU_NUM_ELEMENTS];
PgStat_WalStats wal;
/* to free snapshot in bulk */
MemoryContext context;
struct pgstat_snapshot_hash *stats;
} PgStat_Snapshot;
/*
* Collection of backend-local stats state.
*/
typedef struct PgStat_LocalState
{
PgStat_ShmemControl *shmem;
dsa_area *dsa;
dshash_table *shared_hash;
/* the current statistics snapshot */
PgStat_Snapshot snapshot;
} PgStat_LocalState;
/*
* Inline functions defined further below.
*/
static inline void pgstat_begin_changecount_write(uint32 *cc);
static inline void pgstat_end_changecount_write(uint32 *cc);
static inline uint32 pgstat_begin_changecount_read(uint32 *cc);
static inline bool pgstat_end_changecount_read(uint32 *cc, uint32 cc_before);
static inline void pgstat_copy_changecounted_stats(void *dst, void *src, size_t len,
uint32 *cc);
static inline int pgstat_cmp_hash_key(const void *a, const void *b, size_t size, void *arg);
static inline uint32 pgstat_hash_hash_key(const void *d, size_t size, void *arg);
static inline size_t pgstat_get_entry_len(PgStat_Kind kind);
static inline void *pgstat_get_entry_data(PgStat_Kind kind, PgStatShared_Common *entry);
/*
* Functions in pgstat.c
*/
extern const PgStat_KindInfo *pgstat_get_kind_info(PgStat_Kind kind);
#ifdef USE_ASSERT_CHECKING
extern void pgstat_assert_is_up(void);
#else
#define pgstat_assert_is_up() ((void)true)
#endif
extern void pgstat_delete_pending_entry(PgStat_EntryRef *entry_ref);
extern PgStat_EntryRef *pgstat_prep_pending_entry(PgStat_Kind kind, Oid dboid, Oid objoid, bool *created_entry);
extern PgStat_EntryRef *pgstat_fetch_pending_entry(PgStat_Kind kind, Oid dboid, Oid objoid);
extern void *pgstat_fetch_entry(PgStat_Kind kind, Oid dboid, Oid objoid);
extern void pgstat_snapshot_fixed(PgStat_Kind kind);
/*
* Functions in pgstat_archiver.c
*/
extern void pgstat_archiver_reset_all_cb(TimestampTz ts);
extern void pgstat_archiver_snapshot_cb(void);
/*
* Functions in pgstat_bgwriter.c
*/
extern void pgstat_bgwriter_reset_all_cb(TimestampTz ts);
extern void pgstat_bgwriter_snapshot_cb(void);
/*
* Functions in pgstat_checkpointer.c
*/
extern void pgstat_checkpointer_reset_all_cb(TimestampTz ts);
extern void pgstat_checkpointer_snapshot_cb(void);
/*
* Functions in pgstat_database.c
*/
extern void pgstat_report_disconnect(Oid dboid);
extern void pgstat_update_dbstats(TimestampTz ts);
extern void AtEOXact_PgStat_Database(bool isCommit, bool parallel);
extern PgStat_StatDBEntry *pgstat_prep_database_pending(Oid dboid);
extern void pgstat_reset_database_timestamp(Oid dboid, TimestampTz ts);
extern bool pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
extern void pgstat_database_reset_timestamp_cb(PgStatShared_Common *header, TimestampTz ts);
/*
* Functions in pgstat_function.c
*/
extern bool pgstat_function_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
/*
* Functions in pgstat_io.c
*/
extern bool pgstat_flush_io(bool nowait);
extern void pgstat_io_reset_all_cb(TimestampTz ts);
extern void pgstat_io_snapshot_cb(void);
/*
* Functions in pgstat_relation.c
*/
extern void AtEOXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit);
extern void AtEOSubXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit, int nestDepth);
extern void AtPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state);
extern void PostPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state);
extern bool pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
extern void pgstat_relation_delete_pending_cb(PgStat_EntryRef *entry_ref);
/*
* Functions in pgstat_replslot.c
*/
extern void pgstat_replslot_reset_timestamp_cb(PgStatShared_Common *header, TimestampTz ts);
extern void pgstat_replslot_to_serialized_name_cb(const PgStat_HashKey *key, const PgStatShared_Common *header, NameData *name);
extern bool pgstat_replslot_from_serialized_name_cb(const NameData *name, PgStat_HashKey *key);
/*
* Functions in pgstat_shmem.c
*/
extern void pgstat_attach_shmem(void);
extern void pgstat_detach_shmem(void);
extern PgStat_EntryRef *pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, Oid objoid,
bool create, bool *created_entry);
extern bool pgstat_lock_entry(PgStat_EntryRef *entry_ref, bool nowait);
extern bool pgstat_lock_entry_shared(PgStat_EntryRef *entry_ref, bool nowait);
extern void pgstat_unlock_entry(PgStat_EntryRef *entry_ref);
extern bool pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid);
extern void pgstat_drop_all_entries(void);
extern PgStat_EntryRef *pgstat_get_entry_ref_locked(PgStat_Kind kind, Oid dboid, Oid objoid,
bool nowait);
extern void pgstat_reset_entry(PgStat_Kind kind, Oid dboid, Oid objoid, TimestampTz ts);
extern void pgstat_reset_entries_of_kind(PgStat_Kind kind, TimestampTz ts);
extern void pgstat_reset_matching_entries(bool (*do_reset) (PgStatShared_HashEntry *, Datum),
Datum match_data,
TimestampTz ts);
extern void pgstat_request_entry_refs_gc(void);
extern PgStatShared_Common *pgstat_init_entry(PgStat_Kind kind,
PgStatShared_HashEntry *shhashent);
/*
* Functions in pgstat_slru.c
*/
extern bool pgstat_slru_flush(bool nowait);
extern void pgstat_slru_reset_all_cb(TimestampTz ts);
extern void pgstat_slru_snapshot_cb(void);
/*
* Functions in pgstat_wal.c
*/
extern bool pgstat_flush_wal(bool nowait);
extern void pgstat_init_wal(void);
extern bool pgstat_have_pending_wal(void);
extern void pgstat_wal_reset_all_cb(TimestampTz ts);
extern void pgstat_wal_snapshot_cb(void);
/*
* Functions in pgstat_subscription.c
*/
extern bool pgstat_subscription_flush_cb(PgStat_EntryRef *entry_ref, bool nowait);
extern void pgstat_subscription_reset_timestamp_cb(PgStatShared_Common *header, TimestampTz ts);
/*
* Functions in pgstat_xact.c
*/
extern PgStat_SubXactStatus *pgstat_get_xact_stack_level(int nest_level);
extern void pgstat_drop_transactional(PgStat_Kind kind, Oid dboid, Oid objoid);
extern void pgstat_create_transactional(PgStat_Kind kind, Oid dboid, Oid objoid);
/*
* Variables in pgstat.c
*/
extern PGDLLIMPORT PgStat_LocalState pgStatLocal;
/*
* Variables in pgstat_io.c
*/
extern PGDLLIMPORT bool have_iostats;
/*
* Variables in pgstat_slru.c
*/
extern PGDLLIMPORT bool have_slrustats;
/*
* Implementation of inline functions declared above.
*/
/*
* Helpers for changecount manipulation. See comments around struct
* PgBackendStatus for details.
*/
static inline void
pgstat_begin_changecount_write(uint32 *cc)
{
Assert((*cc & 1) == 0);
START_CRIT_SECTION();
(*cc)++;
pg_write_barrier();
}
static inline void
pgstat_end_changecount_write(uint32 *cc)
{
Assert((*cc & 1) == 1);
pg_write_barrier();
(*cc)++;
END_CRIT_SECTION();
}
static inline uint32
pgstat_begin_changecount_read(uint32 *cc)
{
uint32 before_cc = *cc;
CHECK_FOR_INTERRUPTS();
pg_read_barrier();
return before_cc;
}
/*
* Returns true if the read succeeded, false if it needs to be repeated.
*/
static inline bool
pgstat_end_changecount_read(uint32 *cc, uint32 before_cc)
{
uint32 after_cc;
pg_read_barrier();
after_cc = *cc;
/* was a write in progress when we started? */
if (before_cc & 1)
return false;
/* did writes start and complete while we read? */
return before_cc == after_cc;
}
/*
* helper function for PgStat_KindInfo->snapshot_cb
* PgStat_KindInfo->reset_all_cb callbacks.
*
* Copies out the specified memory area following change-count protocol.
*/
static inline void
pgstat_copy_changecounted_stats(void *dst, void *src, size_t len,
uint32 *cc)
{
uint32 cc_before;
do
{
cc_before = pgstat_begin_changecount_read(cc);
memcpy(dst, src, len);
}
while (!pgstat_end_changecount_read(cc, cc_before));
}
/* helpers for dshash / simplehash hashtables */
static inline int
pgstat_cmp_hash_key(const void *a, const void *b, size_t size, void *arg)
{
Assert(size == sizeof(PgStat_HashKey) && arg == NULL);
return memcmp(a, b, sizeof(PgStat_HashKey));
}
static inline uint32
pgstat_hash_hash_key(const void *d, size_t size, void *arg)
{
const PgStat_HashKey *key = (PgStat_HashKey *) d;
uint32 hash;
Assert(size == sizeof(PgStat_HashKey) && arg == NULL);
hash = murmurhash32(key->kind);
hash = hash_combine(hash, murmurhash32(key->dboid));
hash = hash_combine(hash, murmurhash32(key->objoid));
return hash;
}
/*
* The length of the data portion of a shared memory stats entry (i.e. without
* transient data such as refcounts, lwlocks, ...).
*/
static inline size_t
pgstat_get_entry_len(PgStat_Kind kind)
{
return pgstat_get_kind_info(kind)->shared_data_len;
}
/*
* Returns a pointer to the data portion of a shared memory stats entry.
*/
static inline void *
pgstat_get_entry_data(PgStat_Kind kind, PgStatShared_Common *entry)
{
size_t off = pgstat_get_kind_info(kind)->shared_data_off;
Assert(off != 0 && off < PG_UINT32_MAX);
return ((char *) (entry)) + off;
}
#endif /* PGSTAT_INTERNAL_H */