diff options
Diffstat (limited to 'src/include/access/htup_details.h')
| -rw-r--r-- | src/include/access/htup_details.h | 36 |
1 files changed, 35 insertions, 1 deletions
diff --git a/src/include/access/htup_details.h b/src/include/access/htup_details.h index 0a673cd526..80285acc3b 100644 --- a/src/include/access/htup_details.h +++ b/src/include/access/htup_details.h @@ -96,6 +96,15 @@ * 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 @@ -138,7 +147,8 @@ struct HeapTupleHeaderData DatumTupleFields t_datum; } t_choice; - ItemPointerData t_ctid; /* current TID of this or newer tuple */ + ItemPointerData t_ctid; /* current TID of this or newer tuple (or a + * speculative insertion token) */ /* Fields below here must match MinimalTupleData! */ @@ -242,6 +252,14 @@ struct HeapTupleHeaderData #define HEAP_TUPLE_HAS_MATCH HEAP_ONLY_TUPLE /* tuple has a join match */ /* + * Special value used in t_ctid.ip_posid, to indicate that it holds a + * speculative insertion token rather than a real TID. This must be higher + * than MaxOffsetNumber, so that it can be distinguished from a valid + * offset number in a regular item pointer. + */ +#define SpecTokenOffsetNumber 0xfffe + +/* * HeapTupleHeader accessor macros * * Note: beware of multiple evaluations of "tup" argument. But the Set @@ -377,6 +395,22 @@ do { \ (tup)->t_choice.t_heap.t_field3.t_xvac = (xid); \ } while (0) +#define HeapTupleHeaderIsSpeculative(tup) \ +( \ + (tup)->t_ctid.ip_posid == SpecTokenOffsetNumber \ +) + +#define HeapTupleHeaderGetSpeculativeToken(tup) \ +( \ + AssertMacro(HeapTupleHeaderIsSpeculative(tup)), \ + ItemPointerGetBlockNumber(&(tup)->t_ctid) \ +) + +#define HeapTupleHeaderSetSpeculativeToken(tup, token) \ +( \ + ItemPointerSet(&(tup)->t_ctid, token, SpecTokenOffsetNumber) \ +) + #define HeapTupleHeaderGetDatumLength(tup) \ VARSIZE(tup) |