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db_include/access/htup_details.h Executable file
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/*-------------------------------------------------------------------------
*
* htup_details.h
* POSTGRES heap tuple header definitions.
*
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/htup_details.h
*
*-------------------------------------------------------------------------
*/
#ifndef HTUP_DETAILS_H
#define HTUP_DETAILS_H
#include "access/htup.h"
#include "access/transam.h"
#include "access/tupdesc.h"
#include "access/tupmacs.h"
#include "storage/bufpage.h"
/*
* MaxTupleAttributeNumber limits the number of (user) columns in a tuple.
* The key limit on this value is that the size of the fixed overhead for
* a tuple, plus the size of the null-values bitmap (at 1 bit per column),
* plus MAXALIGN alignment, must fit into t_hoff which is uint8. On most
* machines the upper limit without making t_hoff wider would be a little
* over 1700. We use round numbers here and for MaxHeapAttributeNumber
* so that alterations in HeapTupleHeaderData layout won't change the
* supported max number of columns.
*/
#define MaxTupleAttributeNumber 1664 /* 8 * 208 */
/*
* MaxHeapAttributeNumber limits the number of (user) columns in a table.
* This should be somewhat less than MaxTupleAttributeNumber. It must be
* at least one less, else we will fail to do UPDATEs on a maximal-width
* table (because UPDATE has to form working tuples that include CTID).
* In practice we want some additional daylight so that we can gracefully
* support operations that add hidden "resjunk" columns, for example
* SELECT * FROM wide_table ORDER BY foo, bar, baz.
* In any case, depending on column data types you will likely be running
* into the disk-block-based limit on overall tuple size if you have more
* than a thousand or so columns. TOAST won't help.
*/
#define MaxHeapAttributeNumber 1600 /* 8 * 200 */
/*
* Heap tuple header. To avoid wasting space, the fields should be
* laid out in such a way as to avoid structure padding.
*
* Datums of composite types (row types) share the same general structure
* as on-disk tuples, so that the same routines can be used to build and
* examine them. However the requirements are slightly different: a Datum
* does not need any transaction visibility information, and it does need
* a length word and some embedded type information. We can achieve this
* by overlaying the xmin/cmin/xmax/cmax/xvac fields of a heap tuple
* with the fields needed in the Datum case. Typically, all tuples built
* in-memory will be initialized with the Datum fields; but when a tuple is
* about to be inserted in a table, the transaction fields will be filled,
* overwriting the datum fields.
*
* The overall structure of a heap tuple looks like:
* fixed fields (HeapTupleHeaderData struct)
* nulls bitmap (if HEAP_HASNULL is set in t_infomask)
* alignment padding (as needed to make user data MAXALIGN'd)
* object ID (if HEAP_HASOID_OLD is set in t_infomask, not created
* anymore)
* user data fields
*
* We store five "virtual" fields Xmin, Cmin, Xmax, Cmax, and Xvac in three
* physical fields. Xmin and Xmax are always really stored, but Cmin, Cmax
* and Xvac share a field. This works because we know that Cmin and Cmax
* are only interesting for the lifetime of the inserting and deleting
* transaction respectively. If a tuple is inserted and deleted in the same
* transaction, we store a "combo" command id that can be mapped to the real
* cmin and cmax, but only by use of local state within the originating
* backend. See combocid.c for more details. Meanwhile, Xvac is only set by
* old-style VACUUM FULL, which does not have any command sub-structure and so
* does not need either Cmin or Cmax. (This requires that old-style VACUUM
* FULL never try to move a tuple whose Cmin or Cmax is still interesting,
* ie, an insert-in-progress or delete-in-progress tuple.)
*
* A word about t_ctid: whenever a new tuple is stored on disk, its t_ctid
* is initialized with its own TID (location). If the tuple is ever updated,
* its t_ctid is changed to point to the replacement version of the tuple. Or
* if the tuple is moved from one partition to another, due to an update of
* the partition key, t_ctid is set to a special value to indicate that
* (see ItemPointerSetMovedPartitions). Thus, a tuple is the latest version
* of its row iff XMAX is invalid or
* t_ctid points to itself (in which case, if XMAX is valid, the tuple is
* either locked or deleted). One can follow the chain of t_ctid links
* to find the newest version of the row, unless it was moved to a different
* partition. Beware however that VACUUM might
* erase the pointed-to (newer) tuple before erasing the pointing (older)
* tuple. Hence, when following a t_ctid link, it is necessary to check
* to see if the referenced slot is empty or contains an unrelated tuple.
* Check that the referenced tuple has XMIN equal to the referencing tuple's
* XMAX to verify that it is actually the descendant version and not an
* unrelated tuple stored into a slot recently freed by VACUUM. If either
* check fails, one may assume that there is no live descendant version.
*
* t_ctid is sometimes used to store a speculative insertion token, instead
* of a real TID. A speculative token is set on a tuple that's being
* inserted, until the inserter is sure that it wants to go ahead with the
* insertion. Hence a token should only be seen on a tuple with an XMAX
* that's still in-progress, or invalid/aborted. The token is replaced with
* the tuple's real TID when the insertion is confirmed. One should never
* see a speculative insertion token while following a chain of t_ctid links,
* because they are not used on updates, only insertions.
*
* Following the fixed header fields, the nulls bitmap is stored (beginning
* at t_bits). The bitmap is *not* stored if t_infomask shows that there
* are no nulls in the tuple. If an OID field is present (as indicated by
* t_infomask), then it is stored just before the user data, which begins at
* the offset shown by t_hoff. Note that t_hoff must be a multiple of
* MAXALIGN.
*/
typedef struct HeapTupleFields
{
TransactionId t_xmin; /* inserting xact ID */
TransactionId t_xmax; /* deleting or locking xact ID */
union
{
CommandId t_cid; /* inserting or deleting command ID, or both */
TransactionId t_xvac; /* old-style VACUUM FULL xact ID */
} t_field3;
} HeapTupleFields;
typedef struct DatumTupleFields
{
int32 datum_len_; /* varlena header (do not touch directly!) */
int32 datum_typmod; /* -1, or identifier of a record type */
Oid datum_typeid; /* composite type OID, or RECORDOID */
/*
* datum_typeid cannot be a domain over composite, only plain composite,
* even if the datum is meant as a value of a domain-over-composite type.
* This is in line with the general principle that CoerceToDomain does not
* change the physical representation of the base type value.
*
* Note: field ordering is chosen with thought that Oid might someday
* widen to 64 bits.
*/
} DatumTupleFields;
struct HeapTupleHeaderData
{
union
{
HeapTupleFields t_heap;
DatumTupleFields t_datum;
} t_choice;
ItemPointerData t_ctid; /* current TID of this or newer tuple (or a
* speculative insertion token) */
/* Fields below here must match MinimalTupleData! */
#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK2 2
uint16 t_infomask2; /* number of attributes + various flags */
#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK 3
uint16 t_infomask; /* various flag bits, see below */
#define FIELDNO_HEAPTUPLEHEADERDATA_HOFF 4
uint8 t_hoff; /* sizeof header incl. bitmap, padding */
/* ^ - 23 bytes - ^ */
#define FIELDNO_HEAPTUPLEHEADERDATA_BITS 5
bits8 t_bits[FLEXIBLE_ARRAY_MEMBER]; /* bitmap of NULLs */
/* MORE DATA FOLLOWS AT END OF STRUCT */
};
/* typedef appears in htup.h */
#define SizeofHeapTupleHeader offsetof(HeapTupleHeaderData, t_bits)
/*
* information stored in t_infomask:
*/
#define HEAP_HASNULL 0x0001 /* has null attribute(s) */
#define HEAP_HASVARWIDTH 0x0002 /* has variable-width attribute(s) */
#define HEAP_HASEXTERNAL 0x0004 /* has external stored attribute(s) */
#define HEAP_HASOID_OLD 0x0008 /* has an object-id field */
#define HEAP_XMAX_KEYSHR_LOCK 0x0010 /* xmax is a key-shared locker */
#define HEAP_COMBOCID 0x0020 /* t_cid is a combo CID */
#define HEAP_XMAX_EXCL_LOCK 0x0040 /* xmax is exclusive locker */
#define HEAP_XMAX_LOCK_ONLY 0x0080 /* xmax, if valid, is only a locker */
/* xmax is a shared locker */
#define HEAP_XMAX_SHR_LOCK (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)
#define HEAP_LOCK_MASK (HEAP_XMAX_SHR_LOCK | HEAP_XMAX_EXCL_LOCK | \
HEAP_XMAX_KEYSHR_LOCK)
#define HEAP_XMIN_COMMITTED 0x0100 /* t_xmin committed */
#define HEAP_XMIN_INVALID 0x0200 /* t_xmin invalid/aborted */
#define HEAP_XMIN_FROZEN (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)
#define HEAP_XMAX_COMMITTED 0x0400 /* t_xmax committed */
#define HEAP_XMAX_INVALID 0x0800 /* t_xmax invalid/aborted */
#define HEAP_XMAX_IS_MULTI 0x1000 /* t_xmax is a MultiXactId */
#define HEAP_UPDATED 0x2000 /* this is UPDATEd version of row */
#define HEAP_MOVED_OFF 0x4000 /* moved to another place by pre-9.0
* VACUUM FULL; kept for binary
* upgrade support */
#define HEAP_MOVED_IN 0x8000 /* moved from another place by pre-9.0
* VACUUM FULL; kept for binary
* upgrade support */
#define HEAP_MOVED (HEAP_MOVED_OFF | HEAP_MOVED_IN)
#define HEAP_XACT_MASK 0xFFF0 /* visibility-related bits */
/*
* A tuple is only locked (i.e. not updated by its Xmax) if the
* HEAP_XMAX_LOCK_ONLY bit is set; or, for pg_upgrade's sake, if the Xmax is
* not a multi and the EXCL_LOCK bit is set.
*
* See also HeapTupleHeaderIsOnlyLocked, which also checks for a possible
* aborted updater transaction.
*
* Beware of multiple evaluations of the argument.
*/
#define HEAP_XMAX_IS_LOCKED_ONLY(infomask) \
(((infomask) & HEAP_XMAX_LOCK_ONLY) || \
(((infomask) & (HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK)) == HEAP_XMAX_EXCL_LOCK))
/*
* A tuple that has HEAP_XMAX_IS_MULTI and HEAP_XMAX_LOCK_ONLY but neither of
* HEAP_XMAX_EXCL_LOCK and HEAP_XMAX_KEYSHR_LOCK must come from a tuple that was
* share-locked in 9.2 or earlier and then pg_upgrade'd.
*
* In 9.2 and prior, HEAP_XMAX_IS_MULTI was only set when there were multiple
* FOR SHARE lockers of that tuple. That set HEAP_XMAX_LOCK_ONLY (with a
* different name back then) but neither of HEAP_XMAX_EXCL_LOCK and
* HEAP_XMAX_KEYSHR_LOCK. That combination is no longer possible in 9.3 and
* up, so if we see that combination we know for certain that the tuple was
* locked in an earlier release; since all such lockers are gone (they cannot
* survive through pg_upgrade), such tuples can safely be considered not
* locked.
*
* We must not resolve such multixacts locally, because the result would be
* bogus, regardless of where they stand with respect to the current valid
* multixact range.
*/
#define HEAP_LOCKED_UPGRADED(infomask) \
( \
((infomask) & HEAP_XMAX_IS_MULTI) != 0 && \
((infomask) & HEAP_XMAX_LOCK_ONLY) != 0 && \
(((infomask) & (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)) == 0) \
)
/*
* Use these to test whether a particular lock is applied to a tuple
*/
#define HEAP_XMAX_IS_SHR_LOCKED(infomask) \
(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_SHR_LOCK)
#define HEAP_XMAX_IS_EXCL_LOCKED(infomask) \
(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_EXCL_LOCK)
#define HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) \
(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_KEYSHR_LOCK)
/* turn these all off when Xmax is to change */
#define HEAP_XMAX_BITS (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID | \
HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK | HEAP_XMAX_LOCK_ONLY)
/*
* information stored in t_infomask2:
*/
#define HEAP_NATTS_MASK 0x07FF /* 11 bits for number of attributes */
/* bits 0x1800 are available */
#define HEAP_KEYS_UPDATED 0x2000 /* tuple was updated and key cols
* modified, or tuple deleted */
#define HEAP_HOT_UPDATED 0x4000 /* tuple was HOT-updated */
#define HEAP_ONLY_TUPLE 0x8000 /* this is heap-only tuple */
#define HEAP2_XACT_MASK 0xE000 /* visibility-related bits */
/*
* HEAP_TUPLE_HAS_MATCH is a temporary flag used during hash joins. It is
* only used in tuples that are in the hash table, and those don't need
* any visibility information, so we can overlay it on a visibility flag
* instead of using up a dedicated bit.
*/
#define HEAP_TUPLE_HAS_MATCH HEAP_ONLY_TUPLE /* tuple has a join match */
/*
* HeapTupleHeader accessor macros
*
* Note: beware of multiple evaluations of "tup" argument. But the Set
* macros evaluate their other argument only once.
*/
/*
* HeapTupleHeaderGetRawXmin returns the "raw" xmin field, which is the xid
* originally used to insert the tuple. However, the tuple might actually
* be frozen (via HeapTupleHeaderSetXminFrozen) in which case the tuple's xmin
* is visible to every snapshot. Prior to PostgreSQL 9.4, we actually changed
* the xmin to FrozenTransactionId, and that value may still be encountered
* on disk.
*/
#define HeapTupleHeaderGetRawXmin(tup) \
( \
(tup)->t_choice.t_heap.t_xmin \
)
#define HeapTupleHeaderGetXmin(tup) \
( \
HeapTupleHeaderXminFrozen(tup) ? \
FrozenTransactionId : HeapTupleHeaderGetRawXmin(tup) \
)
#define HeapTupleHeaderSetXmin(tup, xid) \
( \
(tup)->t_choice.t_heap.t_xmin = (xid) \
)
#define HeapTupleHeaderXminCommitted(tup) \
( \
((tup)->t_infomask & HEAP_XMIN_COMMITTED) != 0 \
)
#define HeapTupleHeaderXminInvalid(tup) \
( \
((tup)->t_infomask & (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)) == \
HEAP_XMIN_INVALID \
)
#define HeapTupleHeaderXminFrozen(tup) \
( \
((tup)->t_infomask & (HEAP_XMIN_FROZEN)) == HEAP_XMIN_FROZEN \
)
#define HeapTupleHeaderSetXminCommitted(tup) \
( \
AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
((tup)->t_infomask |= HEAP_XMIN_COMMITTED) \
)
#define HeapTupleHeaderSetXminInvalid(tup) \
( \
AssertMacro(!HeapTupleHeaderXminCommitted(tup)), \
((tup)->t_infomask |= HEAP_XMIN_INVALID) \
)
#define HeapTupleHeaderSetXminFrozen(tup) \
( \
AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
((tup)->t_infomask |= HEAP_XMIN_FROZEN) \
)
/*
* HeapTupleHeaderGetRawXmax gets you the raw Xmax field. To find out the Xid
* that updated a tuple, you might need to resolve the MultiXactId if certain
* bits are set. HeapTupleHeaderGetUpdateXid checks those bits and takes care
* to resolve the MultiXactId if necessary. This might involve multixact I/O,
* so it should only be used if absolutely necessary.
*/
#define HeapTupleHeaderGetUpdateXid(tup) \
( \
(!((tup)->t_infomask & HEAP_XMAX_INVALID) && \
((tup)->t_infomask & HEAP_XMAX_IS_MULTI) && \
!((tup)->t_infomask & HEAP_XMAX_LOCK_ONLY)) ? \
HeapTupleGetUpdateXid(tup) \
: \
HeapTupleHeaderGetRawXmax(tup) \
)
#define HeapTupleHeaderGetRawXmax(tup) \
( \
(tup)->t_choice.t_heap.t_xmax \
)
#define HeapTupleHeaderSetXmax(tup, xid) \
( \
(tup)->t_choice.t_heap.t_xmax = (xid) \
)
/*
* HeapTupleHeaderGetRawCommandId will give you what's in the header whether
* it is useful or not. Most code should use HeapTupleHeaderGetCmin or
* HeapTupleHeaderGetCmax instead, but note that those Assert that you can
* get a legitimate result, ie you are in the originating transaction!
*/
#define HeapTupleHeaderGetRawCommandId(tup) \
( \
(tup)->t_choice.t_heap.t_field3.t_cid \
)
/* SetCmin is reasonably simple since we never need a combo CID */
#define HeapTupleHeaderSetCmin(tup, cid) \
do { \
Assert(!((tup)->t_infomask & HEAP_MOVED)); \
(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
(tup)->t_infomask &= ~HEAP_COMBOCID; \
} while (0)
/* SetCmax must be used after HeapTupleHeaderAdjustCmax; see combocid.c */
#define HeapTupleHeaderSetCmax(tup, cid, iscombo) \
do { \
Assert(!((tup)->t_infomask & HEAP_MOVED)); \
(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
if (iscombo) \
(tup)->t_infomask |= HEAP_COMBOCID; \
else \
(tup)->t_infomask &= ~HEAP_COMBOCID; \
} while (0)
#define HeapTupleHeaderGetXvac(tup) \
( \
((tup)->t_infomask & HEAP_MOVED) ? \
(tup)->t_choice.t_heap.t_field3.t_xvac \
: \
InvalidTransactionId \
)
#define HeapTupleHeaderSetXvac(tup, xid) \
do { \
Assert((tup)->t_infomask & HEAP_MOVED); \
(tup)->t_choice.t_heap.t_field3.t_xvac = (xid); \
} while (0)
#define HeapTupleHeaderIsSpeculative(tup) \
( \
(ItemPointerGetOffsetNumberNoCheck(&(tup)->t_ctid) == SpecTokenOffsetNumber) \
)
#define HeapTupleHeaderGetSpeculativeToken(tup) \
( \
AssertMacro(HeapTupleHeaderIsSpeculative(tup)), \
ItemPointerGetBlockNumber(&(tup)->t_ctid) \
)
#define HeapTupleHeaderSetSpeculativeToken(tup, token) \
( \
ItemPointerSet(&(tup)->t_ctid, token, SpecTokenOffsetNumber) \
)
#define HeapTupleHeaderIndicatesMovedPartitions(tup) \
ItemPointerIndicatesMovedPartitions(&(tup)->t_ctid)
#define HeapTupleHeaderSetMovedPartitions(tup) \
ItemPointerSetMovedPartitions(&(tup)->t_ctid)
#define HeapTupleHeaderGetDatumLength(tup) \
VARSIZE(tup)
#define HeapTupleHeaderSetDatumLength(tup, len) \
SET_VARSIZE(tup, len)
#define HeapTupleHeaderGetTypeId(tup) \
( \
(tup)->t_choice.t_datum.datum_typeid \
)
#define HeapTupleHeaderSetTypeId(tup, typeid) \
( \
(tup)->t_choice.t_datum.datum_typeid = (typeid) \
)
#define HeapTupleHeaderGetTypMod(tup) \
( \
(tup)->t_choice.t_datum.datum_typmod \
)
#define HeapTupleHeaderSetTypMod(tup, typmod) \
( \
(tup)->t_choice.t_datum.datum_typmod = (typmod) \
)
/*
* Note that we stop considering a tuple HOT-updated as soon as it is known
* aborted or the would-be updating transaction is known aborted. For best
* efficiency, check tuple visibility before using this macro, so that the
* INVALID bits will be as up to date as possible.
*/
#define HeapTupleHeaderIsHotUpdated(tup) \
( \
((tup)->t_infomask2 & HEAP_HOT_UPDATED) != 0 && \
((tup)->t_infomask & HEAP_XMAX_INVALID) == 0 && \
!HeapTupleHeaderXminInvalid(tup) \
)
#define HeapTupleHeaderSetHotUpdated(tup) \
( \
(tup)->t_infomask2 |= HEAP_HOT_UPDATED \
)
#define HeapTupleHeaderClearHotUpdated(tup) \
( \
(tup)->t_infomask2 &= ~HEAP_HOT_UPDATED \
)
#define HeapTupleHeaderIsHeapOnly(tup) \
( \
((tup)->t_infomask2 & HEAP_ONLY_TUPLE) != 0 \
)
#define HeapTupleHeaderSetHeapOnly(tup) \
( \
(tup)->t_infomask2 |= HEAP_ONLY_TUPLE \
)
#define HeapTupleHeaderClearHeapOnly(tup) \
( \
(tup)->t_infomask2 &= ~HEAP_ONLY_TUPLE \
)
#define HeapTupleHeaderHasMatch(tup) \
( \
((tup)->t_infomask2 & HEAP_TUPLE_HAS_MATCH) != 0 \
)
#define HeapTupleHeaderSetMatch(tup) \
( \
(tup)->t_infomask2 |= HEAP_TUPLE_HAS_MATCH \
)
#define HeapTupleHeaderClearMatch(tup) \
( \
(tup)->t_infomask2 &= ~HEAP_TUPLE_HAS_MATCH \
)
#define HeapTupleHeaderGetNatts(tup) \
((tup)->t_infomask2 & HEAP_NATTS_MASK)
#define HeapTupleHeaderSetNatts(tup, natts) \
( \
(tup)->t_infomask2 = ((tup)->t_infomask2 & ~HEAP_NATTS_MASK) | (natts) \
)
#define HeapTupleHeaderHasExternal(tup) \
(((tup)->t_infomask & HEAP_HASEXTERNAL) != 0)
/*
* BITMAPLEN(NATTS) -
* Computes size of null bitmap given number of data columns.
*/
#define BITMAPLEN(NATTS) (((int)(NATTS) + 7) / 8)
/*
* MaxHeapTupleSize is the maximum allowed size of a heap tuple, including
* header and MAXALIGN alignment padding. Basically it's BLCKSZ minus the
* other stuff that has to be on a disk page. Since heap pages use no
* "special space", there's no deduction for that.
*
* NOTE: we allow for the ItemId that must point to the tuple, ensuring that
* an otherwise-empty page can indeed hold a tuple of this size. Because
* ItemIds and tuples have different alignment requirements, don't assume that
* you can, say, fit 2 tuples of size MaxHeapTupleSize/2 on the same page.
*/
#define MaxHeapTupleSize (BLCKSZ - MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData)))
#define MinHeapTupleSize MAXALIGN(SizeofHeapTupleHeader)
/*
* MaxHeapTuplesPerPage is an upper bound on the number of tuples that can
* fit on one heap page. (Note that indexes could have more, because they
* use a smaller tuple header.) We arrive at the divisor because each tuple
* must be maxaligned, and it must have an associated line pointer.
*
* Note: with HOT, there could theoretically be more line pointers (not actual
* tuples) than this on a heap page. However we constrain the number of line
* pointers to this anyway, to avoid excessive line-pointer bloat and not
* require increases in the size of work arrays.
*/
#define MaxHeapTuplesPerPage \
((int) ((BLCKSZ - SizeOfPageHeaderData) / \
(MAXALIGN(SizeofHeapTupleHeader) + sizeof(ItemIdData))))
/*
* MaxAttrSize is a somewhat arbitrary upper limit on the declared size of
* data fields of char(n) and similar types. It need not have anything
* directly to do with the *actual* upper limit of varlena values, which
* is currently 1Gb (see TOAST structures in postgres.h). I've set it
* at 10Mb which seems like a reasonable number --- tgl 8/6/00.
*/
#define MaxAttrSize (10 * 1024 * 1024)
/*
* MinimalTuple is an alternative representation that is used for transient
* tuples inside the executor, in places where transaction status information
* is not required, the tuple rowtype is known, and shaving off a few bytes
* is worthwhile because we need to store many tuples. The representation
* is chosen so that tuple access routines can work with either full or
* minimal tuples via a HeapTupleData pointer structure. The access routines
* see no difference, except that they must not access the transaction status
* or t_ctid fields because those aren't there.
*
* For the most part, MinimalTuples should be accessed via TupleTableSlot
* routines. These routines will prevent access to the "system columns"
* and thereby prevent accidental use of the nonexistent fields.
*
* MinimalTupleData contains a length word, some padding, and fields matching
* HeapTupleHeaderData beginning with t_infomask2. The padding is chosen so
* that offsetof(t_infomask2) is the same modulo MAXIMUM_ALIGNOF in both
* structs. This makes data alignment rules equivalent in both cases.
*
* When a minimal tuple is accessed via a HeapTupleData pointer, t_data is
* set to point MINIMAL_TUPLE_OFFSET bytes before the actual start of the
* minimal tuple --- that is, where a full tuple matching the minimal tuple's
* data would start. This trick is what makes the structs seem equivalent.
*
* Note that t_hoff is computed the same as in a full tuple, hence it includes
* the MINIMAL_TUPLE_OFFSET distance. t_len does not include that, however.
*
* MINIMAL_TUPLE_DATA_OFFSET is the offset to the first useful (non-pad) data
* other than the length word. tuplesort.c and tuplestore.c use this to avoid
* writing the padding to disk.
*/
#define MINIMAL_TUPLE_OFFSET \
((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) / MAXIMUM_ALIGNOF * MAXIMUM_ALIGNOF)
#define MINIMAL_TUPLE_PADDING \
((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) % MAXIMUM_ALIGNOF)
#define MINIMAL_TUPLE_DATA_OFFSET \
offsetof(MinimalTupleData, t_infomask2)
struct MinimalTupleData
{
uint32 t_len; /* actual length of minimal tuple */
char mt_padding[MINIMAL_TUPLE_PADDING];
/* Fields below here must match HeapTupleHeaderData! */
uint16 t_infomask2; /* number of attributes + various flags */
uint16 t_infomask; /* various flag bits, see below */
uint8 t_hoff; /* sizeof header incl. bitmap, padding */
/* ^ - 23 bytes - ^ */
bits8 t_bits[FLEXIBLE_ARRAY_MEMBER]; /* bitmap of NULLs */
/* MORE DATA FOLLOWS AT END OF STRUCT */
};
/* typedef appears in htup.h */
#define SizeofMinimalTupleHeader offsetof(MinimalTupleData, t_bits)
/*
* GETSTRUCT - given a HeapTuple pointer, return address of the user data
*/
#define GETSTRUCT(TUP) ((char *) ((TUP)->t_data) + (TUP)->t_data->t_hoff)
/*
* Accessor macros to be used with HeapTuple pointers.
*/
#define HeapTupleHasNulls(tuple) \
(((tuple)->t_data->t_infomask & HEAP_HASNULL) != 0)
#define HeapTupleNoNulls(tuple) \
(!((tuple)->t_data->t_infomask & HEAP_HASNULL))
#define HeapTupleHasVarWidth(tuple) \
(((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH) != 0)
#define HeapTupleAllFixed(tuple) \
(!((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH))
#define HeapTupleHasExternal(tuple) \
(((tuple)->t_data->t_infomask & HEAP_HASEXTERNAL) != 0)
#define HeapTupleIsHotUpdated(tuple) \
HeapTupleHeaderIsHotUpdated((tuple)->t_data)
#define HeapTupleSetHotUpdated(tuple) \
HeapTupleHeaderSetHotUpdated((tuple)->t_data)
#define HeapTupleClearHotUpdated(tuple) \
HeapTupleHeaderClearHotUpdated((tuple)->t_data)
#define HeapTupleIsHeapOnly(tuple) \
HeapTupleHeaderIsHeapOnly((tuple)->t_data)
#define HeapTupleSetHeapOnly(tuple) \
HeapTupleHeaderSetHeapOnly((tuple)->t_data)
#define HeapTupleClearHeapOnly(tuple) \
HeapTupleHeaderClearHeapOnly((tuple)->t_data)
/* ----------------
* fastgetattr
*
* Fetch a user attribute's value as a Datum (might be either a
* value, or a pointer into the data area of the tuple).
*
* This must not be used when a system attribute might be requested.
* Furthermore, the passed attnum MUST be valid. Use heap_getattr()
* instead, if in doubt.
*
* This gets called many times, so we macro the cacheable and NULL
* lookups, and call nocachegetattr() for the rest.
* ----------------
*/
#if !defined(DISABLE_COMPLEX_MACRO)
#define fastgetattr(tup, attnum, tupleDesc, isnull) \
( \
AssertMacro((attnum) > 0), \
(*(isnull) = false), \
HeapTupleNoNulls(tup) ? \
( \
TupleDescAttr((tupleDesc), (attnum)-1)->attcacheoff >= 0 ? \
( \
fetchatt(TupleDescAttr((tupleDesc), (attnum)-1), \
(char *) (tup)->t_data + (tup)->t_data->t_hoff + \
TupleDescAttr((tupleDesc), (attnum)-1)->attcacheoff)\
) \
: \
nocachegetattr((tup), (attnum), (tupleDesc)) \
) \
: \
( \
att_isnull((attnum)-1, (tup)->t_data->t_bits) ? \
( \
(*(isnull) = true), \
(Datum)NULL \
) \
: \
( \
nocachegetattr((tup), (attnum), (tupleDesc)) \
) \
) \
)
#else /* defined(DISABLE_COMPLEX_MACRO) */
extern Datum fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
bool *isnull);
#endif /* defined(DISABLE_COMPLEX_MACRO) */
/* ----------------
* heap_getattr
*
* Extract an attribute of a heap tuple and return it as a Datum.
* This works for either system or user attributes. The given attnum
* is properly range-checked.
*
* If the field in question has a NULL value, we return a zero Datum
* and set *isnull == true. Otherwise, we set *isnull == false.
*
* <tup> is the pointer to the heap tuple. <attnum> is the attribute
* number of the column (field) caller wants. <tupleDesc> is a
* pointer to the structure describing the row and all its fields.
* ----------------
*/
#define heap_getattr(tup, attnum, tupleDesc, isnull) \
( \
((attnum) > 0) ? \
( \
((attnum) > (int) HeapTupleHeaderGetNatts((tup)->t_data)) ? \
getmissingattr((tupleDesc), (attnum), (isnull)) \
: \
fastgetattr((tup), (attnum), (tupleDesc), (isnull)) \
) \
: \
heap_getsysattr((tup), (attnum), (tupleDesc), (isnull)) \
)
/* prototypes for functions in common/heaptuple.c */
extern Size heap_compute_data_size(TupleDesc tupleDesc,
Datum *values, bool *isnull);
extern void heap_fill_tuple(TupleDesc tupleDesc,
Datum *values, bool *isnull,
char *data, Size data_size,
uint16 *infomask, bits8 *bit);
extern bool heap_attisnull(HeapTuple tup, int attnum, TupleDesc tupleDesc);
extern Datum nocachegetattr(HeapTuple tup, int attnum,
TupleDesc att);
extern Datum heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
bool *isnull);
extern Datum getmissingattr(TupleDesc tupleDesc,
int attnum, bool *isnull);
extern HeapTuple heap_copytuple(HeapTuple tuple);
extern void heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest);
extern Datum heap_copy_tuple_as_datum(HeapTuple tuple, TupleDesc tupleDesc);
extern HeapTuple heap_form_tuple(TupleDesc tupleDescriptor,
Datum *values, bool *isnull);
extern HeapTuple heap_modify_tuple(HeapTuple tuple,
TupleDesc tupleDesc,
Datum *replValues,
bool *replIsnull,
bool *doReplace);
extern HeapTuple heap_modify_tuple_by_cols(HeapTuple tuple,
TupleDesc tupleDesc,
int nCols,
int *replCols,
Datum *replValues,
bool *replIsnull);
extern void heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
Datum *values, bool *isnull);
extern void heap_freetuple(HeapTuple htup);
extern MinimalTuple heap_form_minimal_tuple(TupleDesc tupleDescriptor,
Datum *values, bool *isnull);
extern void heap_free_minimal_tuple(MinimalTuple mtup);
extern MinimalTuple heap_copy_minimal_tuple(MinimalTuple mtup);
extern HeapTuple heap_tuple_from_minimal_tuple(MinimalTuple mtup);
extern MinimalTuple minimal_tuple_from_heap_tuple(HeapTuple htup);
extern size_t varsize_any(void *p);
extern HeapTuple heap_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
extern MinimalTuple minimal_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
#endif /* HTUP_DETAILS_H */