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/*------------------------------------------------------------------------- * slot.h * Replication slot management. * * Copyright (c) 2012-2016, PostgreSQL Global Development Group * *------------------------------------------------------------------------- */ #ifndef SLOT_H #define SLOT_H #include "fmgr.h" #include "access/xlog.h" #include "access/xlogreader.h" #include "storage/lwlock.h" #include "storage/shmem.h" #include "storage/spin.h" /* * Behaviour of replication slots, upon release or crash. * * Slots marked as PERSISTENT are crashsafe and will not be dropped when * released. Slots marked as EPHEMERAL will be dropped when released or after * restarts. * * EPHEMERAL slots can be made PERSISTENT by calling ReplicationSlotPersist(). */ typedef enum ReplicationSlotPersistency { RS_PERSISTENT, RS_EPHEMERAL } ReplicationSlotPersistency; /* * On-Disk data of a replication slot, preserved across restarts. */ typedef struct ReplicationSlotPersistentData { /* The slot's identifier */ NameData name; /* database the slot is active on */ Oid database; /* * The slot's behaviour when being dropped (or restored after a crash). */ ReplicationSlotPersistency persistency; /* * xmin horizon for data * * NB: This may represent a value that hasn't been written to disk yet; * see notes for effective_xmin, below. */ TransactionId xmin; /* * xmin horizon for catalog tuples * * NB: This may represent a value that hasn't been written to disk yet; * see notes for effective_xmin, below. */ TransactionId catalog_xmin; /* oldest LSN that might be required by this replication slot */ XLogRecPtr restart_lsn; /* * Oldest LSN that the client has acked receipt for. This is used as the * start_lsn point in case the client doesn't specify one, and also as a * safety measure to jump forwards in case the client specifies a * start_lsn that's further in the past than this value. */ XLogRecPtr confirmed_flush; /* plugin name */ NameData plugin; } ReplicationSlotPersistentData; /* * Shared memory state of a single replication slot. */ typedef struct ReplicationSlot { /* lock, on same cacheline as effective_xmin */ slock_t mutex; /* is this slot defined */ bool in_use; /* Who is streaming out changes for this slot? 0 in unused slots. */ pid_t active_pid; /* any outstanding modifications? */ bool just_dirtied; bool dirty; /* * For logical decoding, it's extremely important that we never remove any * data that's still needed for decoding purposes, even after a crash; * otherwise, decoding will produce wrong answers. Ordinary streaming * replication also needs to prevent old row versions from being removed * too soon, but the worst consequence we might encounter there is * unwanted query cancellations on the standby. Thus, for logical * decoding, this value represents the latest xmin that has actually been * written to disk, whereas for streaming replication, it's just the same * as the persistent value (data.xmin). */ TransactionId effective_xmin; TransactionId effective_catalog_xmin; /* data surviving shutdowns and crashes */ ReplicationSlotPersistentData data; /* is somebody performing io on this slot? */ LWLock io_in_progress_lock; /* all the remaining data is only used for logical slots */ /* * When the client has confirmed flushes >= candidate_xmin_lsn we can * advance the catalog xmin. When restart_valid has been passed, * restart_lsn can be increased. */ TransactionId candidate_catalog_xmin; XLogRecPtr candidate_xmin_lsn; XLogRecPtr candidate_restart_valid; XLogRecPtr candidate_restart_lsn; } ReplicationSlot; #define SlotIsPhysical(slot) (slot->data.database == InvalidOid) #define SlotIsLogical(slot) (slot->data.database != InvalidOid) /* * Shared memory control area for all of replication slots. */ typedef struct ReplicationSlotCtlData { /* * This array should be declared [FLEXIBLE_ARRAY_MEMBER], but for some * reason you can't do that in an otherwise-empty struct. */ ReplicationSlot replication_slots[1]; } ReplicationSlotCtlData; /* * Pointers to shared memory */ extern PGDLLIMPORT ReplicationSlotCtlData *ReplicationSlotCtl; extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot; /* GUCs */ extern PGDLLIMPORT int max_replication_slots; /* shmem initialization functions */ extern Size ReplicationSlotsShmemSize(void); extern void ReplicationSlotsShmemInit(void); /* management of individual slots */ extern void ReplicationSlotCreate(const char *name, bool db_specific, ReplicationSlotPersistency p); extern void ReplicationSlotPersist(void); extern void ReplicationSlotDrop(const char *name); extern void ReplicationSlotAcquire(const char *name); extern void ReplicationSlotRelease(void); extern void ReplicationSlotSave(void); extern void ReplicationSlotMarkDirty(void); /* misc stuff */ extern bool ReplicationSlotValidateName(const char *name, int elevel); extern void ReplicationSlotReserveWal(void); extern void ReplicationSlotsComputeRequiredXmin(bool already_locked); extern void ReplicationSlotsComputeRequiredLSN(void); extern XLogRecPtr ReplicationSlotsComputeLogicalRestartLSN(void); extern bool ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive); extern void StartupReplicationSlots(void); extern void CheckPointReplicationSlots(void); extern void CheckSlotRequirements(void); /* SQL callable functions */ extern Datum pg_create_physical_replication_slot(PG_FUNCTION_ARGS); extern Datum pg_create_logical_replication_slot(PG_FUNCTION_ARGS); extern Datum pg_drop_replication_slot(PG_FUNCTION_ARGS); extern Datum pg_get_replication_slots(PG_FUNCTION_ARGS); #endif /* SLOT_H */