diff options
| author | Tom Lane | 2021-04-05 22:41:09 +0000 |
|---|---|---|
| committer | Tom Lane | 2021-04-05 22:41:21 +0000 |
| commit | 09c1c6ab4bc5764dd69c53ccfd43b2060b1fd090 (patch) | |
| tree | 0b5eacefe5007d52388f475499b018cccd228c0e /src/backend/access/spgist/README | |
| parent | 49f49defe7c0a330cca084de5da14ccdfdafc6a3 (diff) | |
Support INCLUDE'd columns in SP-GiST.
Not much to say here: does what it says on the tin.
We steal a previously-always-zero bit from the nextOffset
field of leaf index tuples in order to track whether there
is a nulls bitmap. Otherwise it works about like included
columns in other index types.
Pavel Borisov, reviewed by Andrey Borodin and Anastasia Lubennikova,
and rather heavily editorialized on by me
Discussion: https://postgr.es/m/CALT9ZEFi-vMp4faht9f9Junb1nO3NOSjhpxTmbm1UGLMsLqiEQ@mail.gmail.com
Diffstat (limited to 'src/backend/access/spgist/README')
| -rw-r--r-- | src/backend/access/spgist/README | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/src/backend/access/spgist/README b/src/backend/access/spgist/README index b55b0738320..7117e02c770 100644 --- a/src/backend/access/spgist/README +++ b/src/backend/access/spgist/README @@ -56,7 +56,7 @@ list and there is no free space on page, then SP-GiST creates a new inner tuple and distributes leaf tuples into a set of lists on, perhaps, several pages. -Inner tuple consists of: +An inner tuple consists of: optional prefix value - all successors must be consistent with it. Example: @@ -67,14 +67,26 @@ Inner tuple consists of: list of nodes, where node is a (label, pointer) pair. Example of a label: a single character for radix tree -Leaf tuple consists of: +A leaf tuple consists of: a leaf value Example: radix tree - the rest of string (postfix) quad and k-d tree - the point itself - ItemPointer to the heap + ItemPointer to the corresponding heap tuple + nextOffset number of next leaf tuple in a chain on a leaf page + + optional nulls bitmask + optional INCLUDE-column values + +For compatibility with pre-v14 indexes, a leaf tuple has a nulls bitmask +only if there are null values (among the leaf value and the INCLUDE values) +*and* there is at least one INCLUDE column. The null-ness of the leaf +value can be inferred from whether the tuple is on a "nulls page" (see below) +so it is not necessary to represent it explicitly. But we include it anyway +in a bitmask used with INCLUDE values, so that standard tuple deconstruction +code can be used. NULLS HANDLING |