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Refactor nbtree insertion scankeys.

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Use dedicated struct to represent nbtree insertion scan keys.  Having a
dedicated struct makes the difference between search type scankeys and
insertion scankeys a lot clearer, and simplifies the signature of
several related functions.  This is based on a suggestion by Andrey
Lepikhov.

Streamline how unique index insertions cache binary search progress.
Cache the state of in-progress binary searches within _bt_check_unique()
for later instead of having callers avoid repeating the binary search in
an ad-hoc manner.  This makes it easy to add a new optimization:
_bt_check_unique() now falls out of its loop immediately in the common
case where it's already clear that there couldn't possibly be a
duplicate.

The new _bt_check_unique() scheme makes it a lot easier to manage cached
binary search effort afterwards, from within _bt_findinsertloc().  This
is needed for the upcoming patch to make nbtree tuples unique by
treating heap TID as a final tiebreaker column.  Unique key binary
searches need to restore lower and upper bounds.  They cannot simply
continue to use the >= lower bound as the offset to insert at, because
the heap TID tiebreaker column must be used in comparisons for the
restored binary search (unlike the original _bt_check_unique() binary
search, where scankey's heap TID column must be omitted).

Author: Peter Geoghegan, Heikki Linnakangas
Reviewed-By: Heikki Linnakangas, Andrey Lepikhov
Discussion: https://postgr.es/m/CAH2-WzmE6AhUdk9NdWBf4K3HjWXZBX3+umC7mH7+WDrKcRtsOw@mail.gmail.com
This commit is contained in:
Peter Geoghegan
2019-03-20 09:30:57 -07:00
parent 550b9d26f8
commit e5adcb789d
9 changed files with 532 additions and 390 deletions
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78
src/include/access/nbtree.h
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@ -319,6 +319,64 @@ typedef struct BTStackData
typedef BTStackData *BTStack;
/*
* BTScanInsert is the btree-private state needed to find an initial position
* for an indexscan, or to insert new tuples -- an "insertion scankey" (not to
* be confused with a search scankey). It's used to descend a B-Tree using
* _bt_search.
*
* When nextkey is false (the usual case), _bt_search and _bt_binsrch will
* locate the first item >= scankey. When nextkey is true, they will locate
* the first item > scan key.
*
* scankeys is an array of scan key entries for attributes that are compared.
* keysz is the size of the array. During insertion, there must be a scan key
* for every attribute, but when starting a regular index scan some can be
* omitted. The array is used as a flexible array member, though it's sized
* in a way that makes it possible to use stack allocations. See
* nbtree/README for full details.
*/
typedef struct BTScanInsertData
{
bool nextkey;
int keysz; /* Size of scankeys array */
ScanKeyData scankeys[INDEX_MAX_KEYS]; /* Must appear last */
} BTScanInsertData;
typedef BTScanInsertData *BTScanInsert;
/*
* BTInsertStateData is a working area used during insertion.
*
* This is filled in after descending the tree to the first leaf page the new
* tuple might belong on. Tracks the current position while performing
* uniqueness check, before we have determined which exact page to insert
* to.
*
* (This should be private to nbtinsert.c, but it's also used by
* _bt_binsrch_insert)
*/
typedef struct BTInsertStateData
{
IndexTuple itup; /* Item we're inserting */
Size itemsz; /* Size of itup -- should be MAXALIGN()'d */
BTScanInsert itup_key; /* Insertion scankey */
/* Buffer containing leaf page we're likely to insert itup on */
Buffer buf;
/*
* Cache of bounds within the current buffer. Only used for insertions
* where _bt_check_unique is called. See _bt_binsrch_insert and
* _bt_findinsertloc for details.
*/
bool bounds_valid;
OffsetNumber low;
OffsetNumber stricthigh;
} BTInsertStateData;
typedef BTInsertStateData *BTInsertState;
/*
* BTScanOpaqueData is the btree-private state needed for an indexscan.
* This consists of preprocessed scan keys (see _bt_preprocess_keys() for
@ -558,16 +616,12 @@ extern int _bt_pagedel(Relation rel, Buffer buf);
/*
* prototypes for functions in nbtsearch.c
*/
extern BTStack _bt_search(Relation rel,
int keysz, ScanKey scankey, bool nextkey,
Buffer *bufP, int access, Snapshot snapshot);
extern Buffer _bt_moveright(Relation rel, Buffer buf, int keysz,
ScanKey scankey, bool nextkey, bool forupdate, BTStack stack,
int access, Snapshot snapshot);
extern OffsetNumber _bt_binsrch(Relation rel, Buffer buf, int keysz,
ScanKey scankey, bool nextkey);
extern int32 _bt_compare(Relation rel, int keysz, ScanKey scankey,
Page page, OffsetNumber offnum);
extern BTStack _bt_search(Relation rel, BTScanInsert key, Buffer *bufP,
int access, Snapshot snapshot);
extern Buffer _bt_moveright(Relation rel, BTScanInsert key, Buffer buf,
bool forupdate, BTStack stack, int access, Snapshot snapshot);
extern OffsetNumber _bt_binsrch_insert(Relation rel, BTInsertState insertstate);
extern int32 _bt_compare(Relation rel, BTScanInsert key, Page page, OffsetNumber offnum);
extern bool _bt_first(IndexScanDesc scan, ScanDirection dir);
extern bool _bt_next(IndexScanDesc scan, ScanDirection dir);
extern Buffer _bt_get_endpoint(Relation rel, uint32 level, bool rightmost,
@ -576,9 +630,7 @@ extern Buffer _bt_get_endpoint(Relation rel, uint32 level, bool rightmost,
/*
* prototypes for functions in nbtutils.c
*/
extern ScanKey _bt_mkscankey(Relation rel, IndexTuple itup);
extern ScanKey _bt_mkscankey_nodata(Relation rel);
extern void _bt_freeskey(ScanKey skey);
extern BTScanInsert _bt_mkscankey(Relation rel, IndexTuple itup);
extern void _bt_freestack(BTStack stack);
extern void _bt_preprocess_array_keys(IndexScanDesc scan);
extern void _bt_start_array_keys(IndexScanDesc scan, ScanDirection dir);