1 /*-------------------------------------------------------------------------
3 * predicate_internals.h
4 * POSTGRES internal predicate locking definitions.
7 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * src/include/storage/predicate_internals.h
12 *-------------------------------------------------------------------------
14 #ifndef PREDICATE_INTERNALS_H
15 #define PREDICATE_INTERNALS_H
17 #include "storage/lock.h"
22 typedef uint64 SerCommitSeqNo;
25 * Reserved commit sequence numbers:
26 * - 0 is reserved to indicate a non-existent SLRU entry; it cannot be
27 * used as a SerCommitSeqNo, even an invalid one
28 * - InvalidSerCommitSeqNo is used to indicate a transaction that
29 * hasn't committed yet, so use a number greater than all valid
30 * ones to make comparison do the expected thing
31 * - RecoverySerCommitSeqNo is used to refer to transactions that
32 * happened before a crash/recovery, since we restart the sequence
33 * at that point. It's earlier than all normal sequence numbers,
34 * and is only used by recovered prepared transactions
36 #define InvalidSerCommitSeqNo ((SerCommitSeqNo) UINT64CONST(0xFFFFFFFFFFFFFFFF))
37 #define RecoverySerCommitSeqNo ((SerCommitSeqNo) 1)
38 #define FirstNormalSerCommitSeqNo ((SerCommitSeqNo) 2)
41 * The SERIALIZABLEXACT struct contains information needed for each
42 * serializable database transaction to support SSI techniques.
44 * A home-grown list is maintained in shared memory to manage these.
45 * An entry is used when the serializable transaction acquires a snapshot.
46 * Unless the transaction is rolled back, this entry must generally remain
47 * until all concurrent transactions have completed. (There are special
48 * optimizations for READ ONLY transactions which often allow them to be
49 * cleaned up earlier.) A transaction which is rolled back is cleaned up
50 * as soon as possible.
52 * Eligibility for cleanup of committed transactions is generally determined
53 * by comparing the transaction's finishedBefore field to
54 * SerializableGlobalXmin.
56 typedef struct SERIALIZABLEXACT
58 VirtualTransactionId vxid; /* The executing process always has one of
60 SerCommitSeqNo commitSeqNo;
61 union /* these values are not both interesting at
64 SerCommitSeqNo earliestOutConflictCommit; /* when committed with
66 SerCommitSeqNo lastCommitBeforeSnapshot; /* when not committed or
69 SHM_QUEUE outConflicts; /* list of write transactions whose data we
71 SHM_QUEUE inConflicts; /* list of read transactions which couldn't
73 SHM_QUEUE predicateLocks; /* list of associated PREDICATELOCK objects */
74 SHM_QUEUE finishedLink; /* list link in
75 * FinishedSerializableTransactions */
78 * for r/o transactions: list of concurrent r/w transactions that we could
79 * potentially have conflicts with, and vice versa for r/w transactions
81 SHM_QUEUE possibleUnsafeConflicts;
83 TransactionId topXid; /* top level xid for the transaction, if one
84 * exists; else invalid */
85 TransactionId finishedBefore; /* invalid means still running; else
86 * the struct expires when no
87 * serializable xids are before this. */
88 TransactionId xmin; /* the transaction's snapshot xmin */
89 uint32 flags; /* OR'd combination of values defined below */
90 int pid; /* pid of associated process */
93 #define SXACT_FLAG_ROLLED_BACK 0x00000001
94 #define SXACT_FLAG_COMMITTED 0x00000002
96 * The following flag actually means that the flagged transaction has a
97 * conflict out *to a transaction which committed ahead of it*. It's hard
98 * to get that into a name of a reasonable length.
100 #define SXACT_FLAG_CONFLICT_OUT 0x00000004
101 #define SXACT_FLAG_READ_ONLY 0x00000008
102 #define SXACT_FLAG_DID_WRITE 0x00000010
103 #define SXACT_FLAG_MARKED_FOR_DEATH 0x00000020
104 #define SXACT_FLAG_DEFERRABLE_WAITING 0x00000040
105 #define SXACT_FLAG_RO_SAFE 0x00000080
106 #define SXACT_FLAG_RO_UNSAFE 0x00000100
107 #define SXACT_FLAG_SUMMARY_CONFLICT_IN 0x00000200
108 #define SXACT_FLAG_SUMMARY_CONFLICT_OUT 0x00000400
109 #define SXACT_FLAG_PREPARED 0x00000800
112 * The following types are used to provide an ad hoc list for holding
113 * SERIALIZABLEXACT objects. An HTAB is overkill, since there is no need to
114 * access these by key -- there are direct pointers to these objects where
115 * needed. If a shared memory list is created, these types can probably be
116 * eliminated in favor of using the general solution.
118 typedef struct PredXactListElementData
121 SERIALIZABLEXACT sxact;
122 } PredXactListElementData;
124 typedef struct PredXactListElementData *PredXactListElement;
126 #define PredXactListElementDataSize \
127 ((Size)MAXALIGN(sizeof(PredXactListElementData)))
129 typedef struct PredXactListData
131 SHM_QUEUE availableList;
132 SHM_QUEUE activeList;
135 * These global variables are maintained when registering and cleaning up
136 * serializable transactions. They must be global across all backends,
137 * but are not needed outside the predicate.c source file. Protected
138 * by SerializableXactHashLock.
140 TransactionId SxactGlobalXmin; /* global xmin for active serializable
142 int SxactGlobalXminCount; /* how many active serializable
143 * transactions have this xmin */
144 int WritableSxactCount; /* how many non-read-only serializable
145 * transactions are active */
146 SerCommitSeqNo LastSxactCommitSeqNo; /* a strictly monotonically
147 * increasing number for
148 * commits of serializable
150 /* Protected by SerializableXactHashLock. */
151 SerCommitSeqNo CanPartialClearThrough; /* can clear predicate locks
152 * and inConflicts for
153 * committed transactions
154 * through this seq no */
155 /* Protected by SerializableFinishedListLock. */
156 SerCommitSeqNo HavePartialClearedThrough; /* have cleared through this
158 SERIALIZABLEXACT *OldCommittedSxact; /* shared copy of dummy sxact */
160 PredXactListElement element;
163 typedef struct PredXactListData *PredXactList;
165 #define PredXactListDataSize \
166 ((Size)MAXALIGN(sizeof(PredXactListData)))
170 * The following types are used to provide lists of rw-conflicts between
171 * pairs of transactions. Since exactly the same information is needed,
172 * they are also used to record possible unsafe transaction relationships
173 * for purposes of identifying safe snapshots for read-only transactions.
175 * When a RWConflictData is not in use to record either type of relationship
176 * between a pair of transactions, it is kept on an "available" list. The
177 * outLink field is used for maintaining that list.
179 typedef struct RWConflictData
181 SHM_QUEUE outLink; /* link for list of conflicts out from a sxact */
182 SHM_QUEUE inLink; /* link for list of conflicts in to a sxact */
183 SERIALIZABLEXACT *sxactOut;
184 SERIALIZABLEXACT *sxactIn;
187 typedef struct RWConflictData *RWConflict;
189 #define RWConflictDataSize \
190 ((Size)MAXALIGN(sizeof(RWConflictData)))
192 typedef struct RWConflictPoolHeaderData
194 SHM_QUEUE availableList;
196 } RWConflictPoolHeaderData;
198 typedef struct RWConflictPoolHeaderData *RWConflictPoolHeader;
200 #define RWConflictPoolHeaderDataSize \
201 ((Size)MAXALIGN(sizeof(RWConflictPoolHeaderData)))
205 * The SERIALIZABLEXIDTAG struct identifies an xid assigned to a serializable
206 * transaction or any of its subtransactions.
208 typedef struct SERIALIZABLEXIDTAG
211 } SERIALIZABLEXIDTAG;
214 * The SERIALIZABLEXID struct provides a link from a TransactionId for a
215 * serializable transaction to the related SERIALIZABLEXACT record, even if
216 * the transaction has completed and its connection has been closed.
218 * These are created as new top level transaction IDs are first assigned to
219 * transactions which are participating in predicate locking. This may
220 * never happen for a particular transaction if it doesn't write anything.
221 * They are removed with their related serializable transaction objects.
223 * The SubTransGetTopmostTransaction method is used where necessary to get
224 * from an XID which might be from a subtransaction to the top level XID.
226 typedef struct SERIALIZABLEXID
229 SERIALIZABLEXIDTAG tag;
232 SERIALIZABLEXACT *myXact; /* pointer to the top level transaction data */
237 * The PREDICATELOCKTARGETTAG struct identifies a database object which can
238 * be the target of predicate locks.
240 * Note that the hash function being used doesn't properly respect tag
241 * length -- it will go to a four byte boundary past the end of the tag.
242 * If you change this struct, make sure any slack space is initialized,
243 * so that any random bytes in the middle or at the end are not included
246 * TODO SSI: If we always use the same fields for the same type of value, we
247 * should rename these. Holding off until it's clear there are no exceptions.
248 * Since indexes are relations with blocks and tuples, it's looking likely that
249 * the rename will be possible. If not, we may need to divide the last field
250 * and use part of it for a target type, so that we know how to interpret the
253 typedef struct PREDICATELOCKTARGETTAG
255 uint32 locktag_field1; /* a 32-bit ID field */
256 uint32 locktag_field2; /* a 32-bit ID field */
257 uint32 locktag_field3; /* a 32-bit ID field */
258 uint32 locktag_field4; /* a 32-bit ID field */
259 uint32 locktag_field5; /* a 32-bit ID field */
260 } PREDICATELOCKTARGETTAG;
263 * The PREDICATELOCKTARGET struct represents a database object on which there
264 * are predicate locks.
266 * A hash list of these objects is maintained in shared memory. An entry is
267 * added when a predicate lock is requested on an object which doesn't
268 * already have one. An entry is removed when the last lock is removed from
271 * Because a particular target might become obsolete, due to update to a new
272 * version, before the reading transaction is obsolete, we need some way to
273 * prevent errors from reuse of a tuple ID. Rather than attempting to clean
274 * up the targets as the related tuples are pruned or vacuumed, we check the
275 * xmin on access. This should be far less costly.
277 typedef struct PREDICATELOCKTARGET
280 PREDICATELOCKTARGETTAG tag; /* unique identifier of lockable object */
283 SHM_QUEUE predicateLocks; /* list of PREDICATELOCK objects assoc. with
284 * predicate lock target */
285 } PREDICATELOCKTARGET;
289 * The PREDICATELOCKTAG struct identifies an individual predicate lock.
291 * It is the combination of predicate lock target (which is a lockable
292 * object) and a serializable transaction which has acquired a lock on that
295 typedef struct PREDICATELOCKTAG
297 PREDICATELOCKTARGET *myTarget;
298 SERIALIZABLEXACT *myXact;
302 * The PREDICATELOCK struct represents an individual lock.
304 * An entry can be created here when the related database object is read, or
305 * by promotion of multiple finer-grained targets. All entries related to a
306 * serializable transaction are removed when that serializable transaction is
307 * cleaned up. Entries can also be removed when they are combined into a
308 * single coarser-grained lock entry.
310 typedef struct PREDICATELOCK
313 PREDICATELOCKTAG tag; /* unique identifier of lock */
316 SHM_QUEUE targetLink; /* list link in PREDICATELOCKTARGET's list of
318 SHM_QUEUE xactLink; /* list link in SERIALIZABLEXACT's list of
320 SerCommitSeqNo commitSeqNo; /* only used for summarized predicate locks */
325 * The LOCALPREDICATELOCK struct represents a local copy of data which is
326 * also present in the PREDICATELOCK table, organized for fast access without
327 * needing to acquire a LWLock. It is strictly for optimization.
329 * Each serializable transaction creates its own local hash table to hold a
330 * collection of these. This information is used to determine when a number
331 * of fine-grained locks should be promoted to a single coarser-grained lock.
332 * The information is maintained more-or-less in parallel to the
333 * PREDICATELOCK data, but because this data is not protected by locks and is
334 * only used in an optimization heuristic, it is allowed to drift in a few
335 * corner cases where maintaining exact data would be expensive.
337 * The hash table is created when the serializable transaction acquires its
338 * snapshot, and its memory is released upon completion of the transaction.
340 typedef struct LOCALPREDICATELOCK
343 PREDICATELOCKTARGETTAG tag; /* unique identifier of lockable object */
346 bool held; /* is lock held, or just its children? */
347 int childLocks; /* number of child locks currently held */
348 } LOCALPREDICATELOCK;
352 * The types of predicate locks which can be acquired.
354 typedef enum PredicateLockTargetType
356 PREDLOCKTAG_RELATION,
359 /* TODO SSI: Other types may be needed for index locking */
360 } PredicateLockTargetType;
364 * This structure is used to quickly capture a copy of all predicate
365 * locks. This is currently used only by the pg_lock_status function,
366 * which in turn is used by the pg_locks view.
368 typedef struct PredicateLockData
371 PREDICATELOCKTARGETTAG *locktags;
372 SERIALIZABLEXACT *xacts;
377 * These macros define how we map logical IDs of lockable objects into the
378 * physical fields of PREDICATELOCKTARGETTAG. Use these to set up values,
379 * rather than accessing the fields directly. Note multiple eval of target!
381 #define SET_PREDICATELOCKTARGETTAG_RELATION(locktag,dboid,reloid) \
382 ((locktag).locktag_field1 = (dboid), \
383 (locktag).locktag_field2 = (reloid), \
384 (locktag).locktag_field3 = InvalidBlockNumber, \
385 (locktag).locktag_field4 = InvalidOffsetNumber, \
386 (locktag).locktag_field5 = InvalidTransactionId)
388 #define SET_PREDICATELOCKTARGETTAG_PAGE(locktag,dboid,reloid,blocknum) \
389 ((locktag).locktag_field1 = (dboid), \
390 (locktag).locktag_field2 = (reloid), \
391 (locktag).locktag_field3 = (blocknum), \
392 (locktag).locktag_field4 = InvalidOffsetNumber, \
393 (locktag).locktag_field5 = InvalidTransactionId)
395 #define SET_PREDICATELOCKTARGETTAG_TUPLE(locktag,dboid,reloid,blocknum,offnum,xmin) \
396 ((locktag).locktag_field1 = (dboid), \
397 (locktag).locktag_field2 = (reloid), \
398 (locktag).locktag_field3 = (blocknum), \
399 (locktag).locktag_field4 = (offnum), \
400 (locktag).locktag_field5 = (xmin))
402 #define GET_PREDICATELOCKTARGETTAG_DB(locktag) \
403 ((Oid) (locktag).locktag_field1)
404 #define GET_PREDICATELOCKTARGETTAG_RELATION(locktag) \
405 ((Oid) (locktag).locktag_field2)
406 #define GET_PREDICATELOCKTARGETTAG_PAGE(locktag) \
407 ((BlockNumber) (locktag).locktag_field3)
408 #define GET_PREDICATELOCKTARGETTAG_OFFSET(locktag) \
409 ((OffsetNumber) (locktag).locktag_field4)
410 #define GET_PREDICATELOCKTARGETTAG_XMIN(locktag) \
411 ((TransactionId) (locktag).locktag_field5)
412 #define GET_PREDICATELOCKTARGETTAG_TYPE(locktag) \
413 (((locktag).locktag_field4 != InvalidOffsetNumber) ? PREDLOCKTAG_TUPLE : \
414 (((locktag).locktag_field3 != InvalidBlockNumber) ? PREDLOCKTAG_PAGE : \
415 PREDLOCKTAG_RELATION))
418 * Two-phase commit statefile records. There are two types: for each
419 * transaction, we generate one per-transaction record and a variable
420 * number of per-predicate-lock records.
422 typedef enum TwoPhasePredicateRecordType
424 TWOPHASEPREDICATERECORD_XACT,
425 TWOPHASEPREDICATERECORD_LOCK
426 } TwoPhasePredicateRecordType;
429 * Per-transaction information to reconstruct a SERIALIZABLEXACT. Not
430 * much is needed because most of it not meaningful for a recovered
431 * prepared transaction.
433 * In particular, we do not record the in and out conflict lists for a
434 * prepared transaction because the associated SERIALIZABLEXACTs will
435 * not be available after recovery. Instead, we simply record the
436 * existence of each type of conflict by setting the transaction's
437 * summary conflict in/out flag.
439 typedef struct TwoPhasePredicateXactRecord
443 } TwoPhasePredicateXactRecord;
446 typedef struct TwoPhasePredicateLockRecord
448 PREDICATELOCKTARGETTAG target;
449 } TwoPhasePredicateLockRecord;
451 typedef struct TwoPhasePredicateRecord
453 TwoPhasePredicateRecordType type;
456 TwoPhasePredicateXactRecord xactRecord;
457 TwoPhasePredicateLockRecord lockRecord;
459 } TwoPhasePredicateRecord;
462 * Define a macro to use for an "empty" SERIALIZABLEXACT reference.
464 #define InvalidSerializableXact ((SERIALIZABLEXACT *) NULL)
468 * Function definitions for functions needing awareness of predicate
471 extern PredicateLockData *GetPredicateLockStatusData(void);
474 #endif /* PREDICATE_INTERNALS_H */