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Rename jsonb_hash_ops to jsonb_path_ops.

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There's no longer much pressure to switch the default GIN opclass for
jsonb, but there was still some unhappiness with the name "jsonb_hash_ops",
since hashing is no longer a distinguishing property of that opclass,
and anyway it seems like a relatively minor detail.  At the suggestion of
Heikki Linnakangas, we'll use "jsonb_path_ops" instead; that captures the
important characteristic that each index entry depends on the entire path
from the document root to the indexed value.

Also add a user-facing explanation of the implementation properties of
these two opclasses.
This commit is contained in:
Tom Lane
2014-05-11 12:06:04 -04:00
parent e136271a94
commit 12e611d43e
12 changed files with 78 additions and 44 deletions
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27
src/backend/utils/adt/jsonb_gin.c
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@ -315,9 +315,9 @@ gin_triconsistent_jsonb(PG_FUNCTION_ARGS)
/*
*
* jsonb_hash_ops GIN opclass support functions
* jsonb_path_ops GIN opclass support functions
*
* In a jsonb_hash_ops index, the GIN keys are uint32 hashes, one per JSON
* In a jsonb_path_ops index, the GIN keys are uint32 hashes, one per JSON
* value; but the JSON key(s) leading to each value are also included in its
* hash computation. This means we can only support containment queries,
* but the index can distinguish, for example, {"foo": 42} from {"bar": 42}
@ -326,7 +326,7 @@ gin_triconsistent_jsonb(PG_FUNCTION_ARGS)
*/
Datum
gin_extract_jsonb_hash(PG_FUNCTION_ARGS)
gin_extract_jsonb_path(PG_FUNCTION_ARGS)
{
Jsonb *jb = PG_GETARG_JSONB(0);
int32 *nentries = (int32 *) PG_GETARG_POINTER(1);
@ -349,7 +349,7 @@ gin_extract_jsonb_hash(PG_FUNCTION_ARGS)
/* Otherwise, use 2 * root count as initial estimate of result size */
entries = (Datum *) palloc(sizeof(Datum) * total);
/* We keep a stack of hashes corresponding to parent key levels */
/* We keep a stack of partial hashes corresponding to parent key levels */
tail.parent = NULL;
tail.hash = 0;
stack = &tail;
@ -439,7 +439,7 @@ gin_extract_jsonb_hash(PG_FUNCTION_ARGS)
}
Datum
gin_extract_jsonb_query_hash(PG_FUNCTION_ARGS)
gin_extract_jsonb_query_path(PG_FUNCTION_ARGS)
{
int32 *nentries = (int32 *) PG_GETARG_POINTER(1);
StrategyNumber strategy = PG_GETARG_UINT16(2);
@ -449,9 +449,9 @@ gin_extract_jsonb_query_hash(PG_FUNCTION_ARGS)
if (strategy != JsonbContainsStrategyNumber)
elog(ERROR, "unrecognized strategy number: %d", strategy);
/* Query is a jsonb, so just apply gin_extract_jsonb_hash ... */
/* Query is a jsonb, so just apply gin_extract_jsonb_path ... */
entries = (Datum *)
DatumGetPointer(DirectFunctionCall2(gin_extract_jsonb_hash,
DatumGetPointer(DirectFunctionCall2(gin_extract_jsonb_path,
PG_GETARG_DATUM(0),
PointerGetDatum(nentries)));
@ -463,7 +463,7 @@ gin_extract_jsonb_query_hash(PG_FUNCTION_ARGS)
}
Datum
gin_consistent_jsonb_hash(PG_FUNCTION_ARGS)
gin_consistent_jsonb_path(PG_FUNCTION_ARGS)
{
bool *check = (bool *) PG_GETARG_POINTER(0);
StrategyNumber strategy = PG_GETARG_UINT16(1);
@ -480,13 +480,12 @@ gin_consistent_jsonb_hash(PG_FUNCTION_ARGS)
elog(ERROR, "unrecognized strategy number: %d", strategy);
/*
* jsonb_hash_ops is necessarily lossy, not only because of hash
* jsonb_path_ops is necessarily lossy, not only because of hash
* collisions but also because it doesn't preserve complete information
* about the structure of the JSON object. Besides, there are some
* special rules around the containment of raw scalar arrays and regular
* arrays that are not handled here. So we must always recheck a match.
* However, if not all of the keys are present, the tuple certainly
* doesn't match.
* special rules around the containment of raw scalars in arrays that are
* not handled here. So we must always recheck a match. However, if not
* all of the keys are present, the tuple certainly doesn't match.
*/
*recheck = true;
for (i = 0; i < nkeys; i++)
@ -502,7 +501,7 @@ gin_consistent_jsonb_hash(PG_FUNCTION_ARGS)
}
Datum
gin_triconsistent_jsonb_hash(PG_FUNCTION_ARGS)
gin_triconsistent_jsonb_path(PG_FUNCTION_ARGS)
{
GinTernaryValue *check = (GinTernaryValue *) PG_GETARG_POINTER(0);
StrategyNumber strategy = PG_GETARG_UINT16(1);