Re: [HACKERS] Schizophrenic coding in gin_extract_jsonb(_hash)
Heikki Linnakangas writes: > gin_extract_jsonb recursively extracts all the elements, keys and values > of any sub-object too, but JB_ROOT_COUNT only counts the top-level elements. Got it. So if the top level is empty, we can exit early, but otherwise we use its length * 2 as a guess at how big the output will be; which will be right if it's an object without further substructure, and otherwise might need enlargement. > (I hope this is made a bit more clear in the comments I added in the > patch I posted this morning) Didn't read that yet, but will incorporate this info into the jsonb_gin patch I'm working on. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Schizophrenic coding in gin_extract_jsonb(_hash)
On 05/07/2014 06:27 PM, Tom Lane wrote: I think you're just proving the point that this code is woefully underdocumented. If there were, somewhere, some comment explaining what the heck JB_ROOT_COUNT actually counts, maybe I wouldn't be asking this question. jsonb.h is certainly not divulging any such information. After having reverse-engineered the convertJsonb code, I think I can explain what JB_ROOT_COUNT is. If the root of the Jsonb datum is an array, it's the number of elements in that top-level array. If it's an object, it's the number of key/value pairs in that top-level object. Some of the elements of that array (or values of the object) can be arrays or objects themselves. gin_extract_jsonb recursively extracts all the elements, keys and values of any sub-object too, but JB_ROOT_COUNT only counts the top-level elements. (I hope this is made a bit more clear in the comments I added in the patch I posted this morning) - Heikki -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Schizophrenic coding in gin_extract_jsonb(_hash)
Peter Geoghegan writes: > On Tue, May 6, 2014 at 8:08 PM, Tom Lane wrote: >> The early-exit code path supposes that JB_ROOT_COUNT is absolutely >> reliable as an indicator that there's nothing in the jsonb value. >> On the other hand, the realloc logic inside the iteration loop implies >> that JB_ROOT_COUNT is just an untrustworthy estimate. Which theory is >> correct? And why is there not a comment to be seen anywhere? If the code >> is correct then this logic is certainly worthy of a comment or three. > JsonbIteratorNext() is passed "false" as its skipNested argument. It's > recursive. And? I think you're just proving the point that this code is woefully underdocumented. If there were, somewhere, some comment explaining what the heck JB_ROOT_COUNT actually counts, maybe I wouldn't be asking this question. jsonb.h is certainly not divulging any such information. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Schizophrenic coding in gin_extract_jsonb(_hash)
On Tue, May 6, 2014 at 8:08 PM, Tom Lane wrote: > The early-exit code path supposes that JB_ROOT_COUNT is absolutely > reliable as an indicator that there's nothing in the jsonb value. > On the other hand, the realloc logic inside the iteration loop implies > that JB_ROOT_COUNT is just an untrustworthy estimate. Which theory is > correct? And why is there not a comment to be seen anywhere? If the code > is correct then this logic is certainly worthy of a comment or three. JsonbIteratorNext() is passed "false" as its skipNested argument. It's recursive. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Schizophrenic coding in gin_extract_jsonb(_hash)
Would someone care to defend this code?
inttotal = 2 * JB_ROOT_COUNT(jb);
...
if (total == 0)
{
*nentries = 0;
PG_RETURN_POINTER(NULL);
}
...
while ((r = JsonbIteratorNext(&it, &v, false)) != WJB_DONE)
{
if (i >= total)
{
total *= 2;
entries = (Datum *) repalloc(entries, sizeof(Datum) * total);
}
The early-exit code path supposes that JB_ROOT_COUNT is absolutely
reliable as an indicator that there's nothing in the jsonb value.
On the other hand, the realloc logic inside the iteration loop implies
that JB_ROOT_COUNT is just an untrustworthy estimate. Which theory is
correct? And why is there not a comment to be seen anywhere? If the code
is correct then this logic is certainly worthy of a comment or three.
regards, tom lane
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