/*
* pgstat_heap -- returns live/dead tuples info in a heap
*/
static Datum
pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
{
HeapScanDesc scan;
HeapTuple tuple;
BlockNumber nblocks;
BlockNumber block = 0; /* next block to count free space in */
BlockNumber tupblock;
Buffer buffer;
pgstattuple_type stat = {0};
/* Disable syncscan because we assume we scan from block zero upwards */
scan = heap_beginscan_strat(rel, SnapshotAny, 0, NULL, true, false);
nblocks = scan->rs_nblocks; /* # blocks to be scanned */
/* scan the relation */
while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
{
CHECK_FOR_INTERRUPTS();
/* must hold a buffer lock to call HeapTupleSatisfiesVisibility */
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
if (HeapTupleSatisfiesVisibility(tuple, SnapshotNow, scan->rs_cbuf))
{
stat.tuple_len += tuple->t_len;
stat.tuple_count++;
}
else
{
stat.dead_tuple_len += tuple->t_len;
stat.dead_tuple_count++;
}
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
/*
* To avoid physically reading the table twice, try to do the
* free-space scan in parallel with the heap scan. However,
* heap_getnext may find no tuples on a given page, so we cannot
* simply examine the pages returned by the heap scan.
*/
tupblock = BlockIdGetBlockNumber(&tuple->t_self.ip_blkid);
while (block <= tupblock)
{
CHECK_FOR_INTERRUPTS();
buffer = ReadBuffer(rel, block);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
UnlockReleaseBuffer(buffer);
block++;
}
}
heap_endscan(scan);
while (block < nblocks)
{
CHECK_FOR_INTERRUPTS();
buffer = ReadBuffer(rel, block);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
UnlockReleaseBuffer(buffer);
block++;
}
relation_close(rel, AccessShareLock);
stat.table_len = (uint64) nblocks *BLCKSZ;
return build_pgstattuple_type(&stat, fcinfo);
}
/*
* systable_beginscan --- set up for heap-or-index scan
*
* rel: catalog to scan, already opened and suitably locked
* indexId: OID of index to conditionally use
* indexOK: if false, forces a heap scan (see notes below)
* snapshot: time qual to use (NULL for a recent catalog snapshot)
* nkeys, key: scan keys
*
* The attribute numbers in the scan key should be set for the heap case.
* If we choose to index, we reset them to 1..n to reference the index
* columns. Note this means there must be one scankey qualification per
* index column! This is checked by the Asserts in the normal, index-using
* case, but won't be checked if the heapscan path is taken.
*
* The routine checks the normal cases for whether an indexscan is safe,
* but caller can make additional checks and pass indexOK=false if needed.
* In standard case indexOK can simply be constant TRUE.
*/
SysScanDesc
systable_beginscan(Relation heapRelation,
Oid indexId,
bool indexOK,
Snapshot snapshot,
int nkeys, ScanKey key)
{
SysScanDesc sysscan;
Relation irel;
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
irel = index_open(indexId, AccessShareLock);
else
irel = NULL;
sysscan = (SysScanDesc) palloc(sizeof(SysScanDescData));
sysscan->heap_rel = heapRelation;
sysscan->irel = irel;
if (snapshot == NULL)
{
Oid relid = RelationGetRelid(heapRelation);
snapshot = RegisterSnapshot(GetCatalogSnapshot(relid));
sysscan->snapshot = snapshot;
}
else
{
/* Caller is responsible for any snapshot. */
sysscan->snapshot = NULL;
}
if (irel)
{
int i;
/* Change attribute numbers to be index column numbers. */
for (i = 0; i < nkeys; i++)
{
int j;
for (j = 0; j < irel->rd_index->indnatts; j++)
{
if (key[i].sk_attno == irel->rd_index->indkey.values[j])
{
key[i].sk_attno = j + 1;
break;
}
}
if (j == irel->rd_index->indnatts)
elog(ERROR, "column is not in index");
}
sysscan->iscan = index_beginscan(heapRelation, irel,
snapshot, nkeys, 0);
index_rescan(sysscan->iscan, key, nkeys, NULL, 0);
sysscan->scan = NULL;
}
else
{
/*
* We disallow synchronized scans when forced to use a heapscan on a
* catalog. In most cases the desired rows are near the front, so
* that the unpredictable start point of a syncscan is a serious
* disadvantage; and there are no compensating advantages, because
* it's unlikely that such scans will occur in parallel.
*/
sysscan->scan = heap_beginscan_strat(heapRelation, snapshot,
nkeys, key,
true, false);
sysscan->iscan = NULL;
}
return sysscan;
}
