Re: Page at a time index scan

Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On Tue, 2 May 2006, Tom Lane wrote:
>> Also, as noted in other contexts, it'd be a good idea if vacuumcleanup
>> was told the total number of heap tuples (GIN needs this), and both
>> steps really ought to be able to find out if it's a full or lazy vacuum.

> It's already in IndexVacuumCleanupInfo, isn't it?

Yeah, I had forgotten that, but just noticed it again now. The patch
I'm working on at the moment defines

/*
* Struct for input arguments passed to ambulkdelete and amvacuumcleanup
*
* Note that num_heap_tuples will not be valid during ambulkdelete,
* only amvacuumcleanup.
*/
typedef struct IndexVacuumInfo
{
Relation index; /* the index being vacuumed */
bool vacuum_full; /* VACUUM FULL (we have exclusive lock) */
int message_level; /* ereport level for progress messages */
double num_heap_tuples; /* tuples remaining in heap */
} IndexVacuumInfo;

with

IndexBulkDeleteResult *
ambulkdelete (IndexVacuumInfo *info,
IndexBulkDeleteResult *stats,
IndexBulkDeleteCallback callback,
void *callback_state);

Because of limited <varname>maintenance_work_mem</>,
<function>ambulkdelete</> may need to be called more than once when many
tuples are to be deleted. The <literal>stats</> argument is the result
of the previous call for this index (it is NULL for the first call within a
<command>VACUUM</> operation). This allows the AM to accumulate statistics
across the whole operation. Typically, <function>ambulkdelete</> will
modify and return the same struct if the passed <literal>stats</> is not
null.

IndexBulkDeleteResult *
amvacuumcleanup (IndexVacuumInfo *info,
IndexBulkDeleteResult *stats);

Clean up after a <command>VACUUM</command> operation (zero or more
<function>ambulkdelete</> calls). This does not have to do anything
beyond returning index statistics, but it may perform bulk cleanup
such as reclaiming empty index pages. <literal>stats</> is whatever the
last <function>ambulkdelete</> call returned, or NULL if
<function>ambulkdelete</> was not called because no tuples needed to be
deleted. If the result is not NULL it must be a palloc'd struct.
The statistics it contains will be reported by <command>VACUUM</> if
<literal>VERBOSE</> is given.

> BTW: Is it possible to have a partial gist index? If it is,
> num_index_tuples = num_heap_tuples isn't right.

It is, and it isn't ;-). We'll need to see about fixing that.

regards, tom lane