index 33f94c03b2a080a3b7524edf1afdf1b95bf1fe2f..6f806fda8515c1c0dde5662ad71cc5ff4e59fb53 100644 (file)
/*
* XXX Really stupid implementation: this just lossifies pages in
* essentially random order. We should be paying some attention to the
- * number of bits set in each page, instead. Also it might be a good idea
- * to lossify more than the minimum number of pages during each call.
+ * number of bits set in each page, instead.
+ *
+ * Since we are called as soon as nentries exceeds maxentries, we should
+ * push nentries down to significantly less than maxentries, or else we'll
+ * just end up doing this again very soon. We shoot for maxentries/2.
*/
Assert(!tbm->iterating);
Assert(tbm->status == TBM_HASH);
/* This does the dirty work ... */
tbm_mark_page_lossy(tbm, page->blockno);
- if (tbm->nentries <= tbm->maxentries)
+ if (tbm->nentries <= tbm->maxentries / 2)
{
/* we have done enough */
hash_seq_term(&status);
* not care whether we visit lossy chunks or not.
*/
}
+
+ /*
+ * With a big bitmap and small work_mem, it's possible that we cannot
+ * get under maxentries. Again, if that happens, we'd end up uselessly
+ * calling tbm_lossify over and over. To prevent this from becoming a
+ * performance sink, force maxentries up to at least double the current
+ * number of entries. (In essence, we're admitting inability to fit
+ * within work_mem when we do this.) Note that this test will not fire
+ * if we broke out of the loop early; and if we didn't, the current
+ * number of entries is simply not reducible any further.
+ */
+ if (tbm->nentries > tbm->maxentries / 2)
+ tbm->maxentries = Min(tbm->nentries, (INT_MAX - 1) / 2) * 2;
}
/*