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/*-------------------------------------------------------------------------
*
* predicate_internals.h
* POSTGRES internal predicate locking definitions.
*
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/predicate_internals.h
*
*-------------------------------------------------------------------------
*/
#ifndef PREDICATE_INTERNALS_H
#define PREDICATE_INTERNALS_H
#include "storage/lock.h"
/*
* Commit number.
*/
typedef uint64 SerCommitSeqNo;
/*
* Reserved commit sequence numbers:
* - 0 is reserved to indicate a non-existent SLRU entry; it cannot be
* used as a SerCommitSeqNo, even an invalid one
* - InvalidSerCommitSeqNo is used to indicate a transaction that
* hasn't committed yet, so use a number greater than all valid
* ones to make comparison do the expected thing
* - RecoverySerCommitSeqNo is used to refer to transactions that
* happened before a crash/recovery, since we restart the sequence
* at that point. It's earlier than all normal sequence numbers,
* and is only used by recovered prepared transactions
*/
#define InvalidSerCommitSeqNo ((SerCommitSeqNo) PG_UINT64_MAX)
#define RecoverySerCommitSeqNo ((SerCommitSeqNo) 1)
#define FirstNormalSerCommitSeqNo ((SerCommitSeqNo) 2)
/*
* The SERIALIZABLEXACT struct contains information needed for each
* serializable database transaction to support SSI techniques.
*
* A home-grown list is maintained in shared memory to manage these.
* An entry is used when the serializable transaction acquires a snapshot.
* Unless the transaction is rolled back, this entry must generally remain
* until all concurrent transactions have completed. (There are special
* optimizations for READ ONLY transactions which often allow them to be
* cleaned up earlier.) A transaction which is rolled back is cleaned up
* as soon as possible.
*
* Eligibility for cleanup of committed transactions is generally determined
* by comparing the transaction's finishedBefore field to
* SerializableGlobalXmin.
*/
typedef struct SERIALIZABLEXACT
{
VirtualTransactionId vxid; /* The executing process always has one of
* these. */
/*
* We use two numbers to track the order that transactions commit. Before
* commit, a transaction is marked as prepared, and prepareSeqNo is set.
* Shortly after commit, it's marked as committed, and commitSeqNo is set.
* This doesn't give a strict commit order, but these two values together
* are good enough for us, as we can always err on the safe side and
* assume that there's a conflict, if we can't be sure of the exact
* ordering of two commits.
*
* Note that a transaction is marked as prepared for a short period during
* commit processing, even if two-phase commit is not used. But with
* two-phase commit, a transaction can stay in prepared state for some
* time.
*/
SerCommitSeqNo prepareSeqNo;
SerCommitSeqNo commitSeqNo;
/* these values are not both interesting at the same time */
union
{
SerCommitSeqNo earliestOutConflictCommit; /* when committed with
* conflict out */
SerCommitSeqNo lastCommitBeforeSnapshot; /* when not committed or
* no conflict out */
} SeqNo;
SHM_QUEUE outConflicts; /* list of write transactions whose data we
* couldn't read. */
SHM_QUEUE inConflicts; /* list of read transactions which couldn't
* see our write. */
SHM_QUEUE predicateLocks; /* list of associated PREDICATELOCK objects */
SHM_QUEUE finishedLink; /* list link in
* FinishedSerializableTransactions */
/*
* for r/o transactions: list of concurrent r/w transactions that we could
* potentially have conflicts with, and vice versa for r/w transactions
*/
SHM_QUEUE possibleUnsafeConflicts;
TransactionId topXid; /* top level xid for the transaction, if one
* exists; else invalid */
TransactionId finishedBefore; /* invalid means still running; else
* the struct expires when no
* serializable xids are before this. */
TransactionId xmin; /* the transaction's snapshot xmin */
uint32 flags; /* OR'd combination of values defined below */
int pid; /* pid of associated process */
} SERIALIZABLEXACT;
#define SXACT_FLAG_COMMITTED 0x00000001 /* already committed */
#define SXACT_FLAG_PREPARED 0x00000002 /* about to commit */
#define SXACT_FLAG_ROLLED_BACK 0x00000004 /* already rolled back */
#define SXACT_FLAG_DOOMED 0x00000008 /* will roll back */
/*
* The following flag actually means that the flagged transaction has a
* conflict out *to a transaction which committed ahead of it*. It's hard
* to get that into a name of a reasonable length.
*/
#define SXACT_FLAG_CONFLICT_OUT 0x00000010
#define SXACT_FLAG_READ_ONLY 0x00000020
#define SXACT_FLAG_DEFERRABLE_WAITING 0x00000040
#define SXACT_FLAG_RO_SAFE 0x00000080
#define SXACT_FLAG_RO_UNSAFE 0x00000100
#define SXACT_FLAG_SUMMARY_CONFLICT_IN 0x00000200
#define SXACT_FLAG_SUMMARY_CONFLICT_OUT 0x00000400
/*
* The following types are used to provide an ad hoc list for holding
* SERIALIZABLEXACT objects. An HTAB is overkill, since there is no need to
* access these by key -- there are direct pointers to these objects where
* needed. If a shared memory list is created, these types can probably be
* eliminated in favor of using the general solution.
*/
typedef struct PredXactListElementData
{
SHM_QUEUE link;
SERIALIZABLEXACT sxact;
} PredXactListElementData;
typedef struct PredXactListElementData *PredXactListElement;
#define PredXactListElementDataSize \
((Size)MAXALIGN(sizeof(PredXactListElementData)))
typedef struct PredXactListData
{
SHM_QUEUE availableList;
SHM_QUEUE activeList;
/*
* These global variables are maintained when registering and cleaning up
* serializable transactions. They must be global across all backends,
* but are not needed outside the predicate.c source file. Protected by
* SerializableXactHashLock.
*/
TransactionId SxactGlobalXmin; /* global xmin for active serializable
* transactions */
int SxactGlobalXminCount; /* how many active serializable
* transactions have this xmin */
int WritableSxactCount; /* how many non-read-only serializable
* transactions are active */
SerCommitSeqNo LastSxactCommitSeqNo; /* a strictly monotonically
* increasing number for
* commits of serializable
* transactions */
/* Protected by SerializableXactHashLock. */
SerCommitSeqNo CanPartialClearThrough; /* can clear predicate locks
* and inConflicts for
* committed transactions
* through this seq no */
/* Protected by SerializableFinishedListLock. */
SerCommitSeqNo HavePartialClearedThrough; /* have cleared through this
* seq no */
SERIALIZABLEXACT *OldCommittedSxact; /* shared copy of dummy sxact */
PredXactListElement element;
} PredXactListData;
typedef struct PredXactListData *PredXactList;
#define PredXactListDataSize \
((Size)MAXALIGN(sizeof(PredXactListData)))
/*
* The following types are used to provide lists of rw-conflicts between
* pairs of transactions. Since exactly the same information is needed,
* they are also used to record possible unsafe transaction relationships
* for purposes of identifying safe snapshots for read-only transactions.
*
* When a RWConflictData is not in use to record either type of relationship
* between a pair of transactions, it is kept on an "available" list. The
* outLink field is used for maintaining that list.
*/
typedef struct RWConflictData
{
SHM_QUEUE outLink; /* link for list of conflicts out from a sxact */
SHM_QUEUE inLink; /* link for list of conflicts in to a sxact */
SERIALIZABLEXACT *sxactOut;
SERIALIZABLEXACT *sxactIn;
} RWConflictData;
typedef struct RWConflictData *RWConflict;
#define RWConflictDataSize \
((Size)MAXALIGN(sizeof(RWConflictData)))
typedef struct RWConflictPoolHeaderData
{
SHM_QUEUE availableList;
RWConflict element;
} RWConflictPoolHeaderData;
typedef struct RWConflictPoolHeaderData *RWConflictPoolHeader;
#define RWConflictPoolHeaderDataSize \
((Size)MAXALIGN(sizeof(RWConflictPoolHeaderData)))
/*
* The SERIALIZABLEXIDTAG struct identifies an xid assigned to a serializable
* transaction or any of its subtransactions.
*/
typedef struct SERIALIZABLEXIDTAG
{
TransactionId xid;
} SERIALIZABLEXIDTAG;
/*
* The SERIALIZABLEXID struct provides a link from a TransactionId for a
* serializable transaction to the related SERIALIZABLEXACT record, even if
* the transaction has completed and its connection has been closed.
*
* These are created as new top level transaction IDs are first assigned to
* transactions which are participating in predicate locking. This may
* never happen for a particular transaction if it doesn't write anything.
* They are removed with their related serializable transaction objects.
*
* The SubTransGetTopmostTransaction method is used where necessary to get
* from an XID which might be from a subtransaction to the top level XID.
*/
typedef struct SERIALIZABLEXID
{
/* hash key */
SERIALIZABLEXIDTAG tag;
/* data */
SERIALIZABLEXACT *myXact; /* pointer to the top level transaction data */
} SERIALIZABLEXID;
/*
* The PREDICATELOCKTARGETTAG struct identifies a database object which can
* be the target of predicate locks.
*
* Note that the hash function being used doesn't properly respect tag
* length -- if the length of the structure isn't a multiple of four bytes it
* will go to a four byte boundary past the end of the tag. If you change
* this struct, make sure any slack space is initialized, so that any random
* bytes in the middle or at the end are not included in the hash.
*
* TODO SSI: If we always use the same fields for the same type of value, we
* should rename these. Holding off until it's clear there are no exceptions.
* Since indexes are relations with blocks and tuples, it's looking likely that
* the rename will be possible. If not, we may need to divide the last field
* and use part of it for a target type, so that we know how to interpret the
* data..
*/
typedef struct PREDICATELOCKTARGETTAG
{
uint32 locktag_field1; /* a 32-bit ID field */
uint32 locktag_field2; /* a 32-bit ID field */
uint32 locktag_field3; /* a 32-bit ID field */
uint32 locktag_field4; /* a 32-bit ID field */
} PREDICATELOCKTARGETTAG;
/*
* The PREDICATELOCKTARGET struct represents a database object on which there
* are predicate locks.
*
* A hash list of these objects is maintained in shared memory. An entry is
* added when a predicate lock is requested on an object which doesn't
* already have one. An entry is removed when the last lock is removed from
* its list.
*/
typedef struct PREDICATELOCKTARGET
{
/* hash key */
PREDICATELOCKTARGETTAG tag; /* unique identifier of lockable object */
/* data */
SHM_QUEUE predicateLocks; /* list of PREDICATELOCK objects assoc. with
* predicate lock target */
} PREDICATELOCKTARGET;
/*
* The PREDICATELOCKTAG struct identifies an individual predicate lock.
*
* It is the combination of predicate lock target (which is a lockable
* object) and a serializable transaction which has acquired a lock on that
* target.
*/
typedef struct PREDICATELOCKTAG
{
PREDICATELOCKTARGET *myTarget;
SERIALIZABLEXACT *myXact;
} PREDICATELOCKTAG;
/*
* The PREDICATELOCK struct represents an individual lock.
*
* An entry can be created here when the related database object is read, or
* by promotion of multiple finer-grained targets. All entries related to a
* serializable transaction are removed when that serializable transaction is
* cleaned up. Entries can also be removed when they are combined into a
* single coarser-grained lock entry.
*/
typedef struct PREDICATELOCK
{
/* hash key */
PREDICATELOCKTAG tag; /* unique identifier of lock */
/* data */
SHM_QUEUE targetLink; /* list link in PREDICATELOCKTARGET's list of
* predicate locks */
SHM_QUEUE xactLink; /* list link in SERIALIZABLEXACT's list of
* predicate locks */
SerCommitSeqNo commitSeqNo; /* only used for summarized predicate locks */
} PREDICATELOCK;
/*
* The LOCALPREDICATELOCK struct represents a local copy of data which is
* also present in the PREDICATELOCK table, organized for fast access without
* needing to acquire a LWLock. It is strictly for optimization.
*
* Each serializable transaction creates its own local hash table to hold a
* collection of these. This information is used to determine when a number
* of fine-grained locks should be promoted to a single coarser-grained lock.
* The information is maintained more-or-less in parallel to the
* PREDICATELOCK data, but because this data is not protected by locks and is
* only used in an optimization heuristic, it is allowed to drift in a few
* corner cases where maintaining exact data would be expensive.
*
* The hash table is created when the serializable transaction acquires its
* snapshot, and its memory is released upon completion of the transaction.
*/
typedef struct LOCALPREDICATELOCK
{
/* hash key */
PREDICATELOCKTARGETTAG tag; /* unique identifier of lockable object */
/* data */
bool held; /* is lock held, or just its children? */
int childLocks; /* number of child locks currently held */
} LOCALPREDICATELOCK;
/*
* The types of predicate locks which can be acquired.
*/
typedef enum PredicateLockTargetType
{
PREDLOCKTAG_RELATION,
PREDLOCKTAG_PAGE,
PREDLOCKTAG_TUPLE
/* TODO SSI: Other types may be needed for index locking */
} PredicateLockTargetType;
/*
* This structure is used to quickly capture a copy of all predicate
* locks. This is currently used only by the pg_lock_status function,
* which in turn is used by the pg_locks view.
*/
typedef struct PredicateLockData
{
int nelements;
PREDICATELOCKTARGETTAG *locktags;
SERIALIZABLEXACT *xacts;
} PredicateLockData;
/*
* These macros define how we map logical IDs of lockable objects into the
* physical fields of PREDICATELOCKTARGETTAG. Use these to set up values,
* rather than accessing the fields directly. Note multiple eval of target!
*/
#define SET_PREDICATELOCKTARGETTAG_RELATION(locktag,dboid,reloid) \
((locktag).locktag_field1 = (dboid), \
(locktag).locktag_field2 = (reloid), \
(locktag).locktag_field3 = InvalidBlockNumber, \
(locktag).locktag_field4 = InvalidOffsetNumber)
#define SET_PREDICATELOCKTARGETTAG_PAGE(locktag,dboid,reloid,blocknum) \
((locktag).locktag_field1 = (dboid), \
(locktag).locktag_field2 = (reloid), \
(locktag).locktag_field3 = (blocknum), \
(locktag).locktag_field4 = InvalidOffsetNumber)
#define SET_PREDICATELOCKTARGETTAG_TUPLE(locktag,dboid,reloid,blocknum,offnum) \
((locktag).locktag_field1 = (dboid), \
(locktag).locktag_field2 = (reloid), \
(locktag).locktag_field3 = (blocknum), \
(locktag).locktag_field4 = (offnum))
#define GET_PREDICATELOCKTARGETTAG_DB(locktag) \
((Oid) (locktag).locktag_field1)
#define GET_PREDICATELOCKTARGETTAG_RELATION(locktag) \
((Oid) (locktag).locktag_field2)
#define GET_PREDICATELOCKTARGETTAG_PAGE(locktag) \
((BlockNumber) (locktag).locktag_field3)
#define GET_PREDICATELOCKTARGETTAG_OFFSET(locktag) \
((OffsetNumber) (locktag).locktag_field4)
#define GET_PREDICATELOCKTARGETTAG_TYPE(locktag) \
(((locktag).locktag_field4 != InvalidOffsetNumber) ? PREDLOCKTAG_TUPLE : \
(((locktag).locktag_field3 != InvalidBlockNumber) ? PREDLOCKTAG_PAGE : \
PREDLOCKTAG_RELATION))
/*
* Two-phase commit statefile records. There are two types: for each
* transaction, we generate one per-transaction record and a variable
* number of per-predicate-lock records.
*/
typedef enum TwoPhasePredicateRecordType
{
TWOPHASEPREDICATERECORD_XACT,
TWOPHASEPREDICATERECORD_LOCK
} TwoPhasePredicateRecordType;
/*
* Per-transaction information to reconstruct a SERIALIZABLEXACT. Not
* much is needed because most of it not meaningful for a recovered
* prepared transaction.
*
* In particular, we do not record the in and out conflict lists for a
* prepared transaction because the associated SERIALIZABLEXACTs will
* not be available after recovery. Instead, we simply record the
* existence of each type of conflict by setting the transaction's
* summary conflict in/out flag.
*/
typedef struct TwoPhasePredicateXactRecord
{
TransactionId xmin;
uint32 flags;
} TwoPhasePredicateXactRecord;
/* Per-lock state */
typedef struct TwoPhasePredicateLockRecord
{
PREDICATELOCKTARGETTAG target;
uint32 filler; /* to avoid length change in back-patched fix */
} TwoPhasePredicateLockRecord;
typedef struct TwoPhasePredicateRecord
{
TwoPhasePredicateRecordType type;
union
{
TwoPhasePredicateXactRecord xactRecord;
TwoPhasePredicateLockRecord lockRecord;
} data;
} TwoPhasePredicateRecord;
/*
* Define a macro to use for an "empty" SERIALIZABLEXACT reference.
*/
#define InvalidSerializableXact ((SERIALIZABLEXACT *) NULL)
/*
* Function definitions for functions needing awareness of predicate
* locking internals.
*/
extern PredicateLockData *GetPredicateLockStatusData(void);
#endif /* PREDICATE_INTERNALS_H */
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