diff options
Diffstat (limited to 'src/include/nodes/plannodes.h')
| -rw-r--r-- | src/include/nodes/plannodes.h | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h index 13e07ead31..aa11dcedab 100644 --- a/src/include/nodes/plannodes.h +++ b/src/include/nodes/plannodes.h @@ -420,15 +420,28 @@ typedef struct IndexScan * index-only scan, in which the data comes from the index not the heap. * Because of this, *all* Vars in the plan node's targetlist, qual, and * index expressions reference index columns and have varno = INDEX_VAR. - * Hence we do not need separate indexqualorig and indexorderbyorig lists, - * since their contents would be equivalent to indexqual and indexorderby. + * + * We could almost use indexqual directly against the index's output tuple + * when rechecking lossy index operators, but that won't work for quals on + * index columns that are not retrievable. Hence, recheckqual is needed + * for rechecks: it expresses the same condition as indexqual, but using + * only index columns that are retrievable. (We will not generate an + * index-only scan if this is not possible. An example is that if an + * index has table column "x" in a retrievable index column "ind1", plus + * an expression f(x) in a non-retrievable column "ind2", an indexable + * query on f(x) will use "ind2" in indexqual and f(ind1) in recheckqual. + * Without the "ind1" column, an index-only scan would be disallowed.) + * + * We don't currently need a recheckable equivalent of indexorderby, + * because we don't support lossy operators in index ORDER BY. * * To help EXPLAIN interpret the index Vars for display, we provide * indextlist, which represents the contents of the index as a targetlist * with one TLE per index column. Vars appearing in this list reference * the base table, and this is the only field in the plan node that may - * contain such Vars. Note however that index columns that the AM can't - * reconstruct are replaced by null Consts in indextlist. + * contain such Vars. Also, for the convenience of setrefs.c, TLEs in + * indextlist are marked as resjunk if they correspond to columns that + * the index AM cannot reconstruct. * ---------------- */ typedef struct IndexOnlyScan @@ -436,6 +449,7 @@ typedef struct IndexOnlyScan Scan scan; Oid indexid; /* OID of index to scan */ List *indexqual; /* list of index quals (usually OpExprs) */ + List *recheckqual; /* index quals in recheckable form */ List *indexorderby; /* list of index ORDER BY exprs */ List *indextlist; /* TargetEntry list describing index's cols */ ScanDirection indexorderdir; /* forward or backward or don't care */ |