wgtmac commented on code in PR #2406:
URL: https://github.com/apache/orc/pull/2406#discussion_r2358389192
##########
c++/src/Reader.cc:
##########
@@ -1138,13 +1171,37 @@ namespace orc {
if (currentStripe_ < lastStripe_) {
if (enableAsyncPrefetch_) {
- // FIXME: this is very coarse since I/O ranges of all selected columns
are about to
- // prefetch. We can further evaluate index stream with knowledge of
pruned row groups
- // to issue less I/O ranges.
- auto ranges = extractReadRangesForStripe(currentStripe_,
currentStripeInfo_,
- currentStripeFooter_,
selectedColumns_);
+ if (fullyCachedStripes_.find(currentStripe_) !=
fullyCachedStripes_.cend()) {
+ // Current stripe has been fully cached, do nothing.
+ } else if (isSmallStripe(currentStripeInfo_,
contents_->cacheOptions.rangeSizeLimit)) {
+ std::vector<ReadRange> ranges;
+ uint64_t maxStripe =
+ std::min(lastStripe_, currentStripe_ +
smallStripeLookAheadLimit_ + 1);
+ for (uint64_t stripe = currentStripe_; stripe < maxStripe; stripe++)
{
+ const auto& stripeInfo =
footer_->stripes(static_cast<int>(stripe));
+ if (!isSmallStripe(stripeInfo,
contents_->cacheOptions.rangeSizeLimit)) {
+ break;
+ }
+ ranges.push_back(ReadRange{stripeInfo.offset(),
getStripeSize(stripeInfo)});
+ fullyCachedStripes_.insert(stripe);
+ }
+ contents_->cacheRanges(std::move(ranges));
+ } else {
+ // This is very coarse since I/O ranges of all selected columns are
about to prefetch.
+ // We can further evaluate index stream with knowledge of pruned row
groups to issue
+ // less I/O ranges.
+ contents_->cacheRanges(extractReadRangesForStripe(
+ currentStripe_, currentStripeInfo_, currentStripeFooter_,
selectedColumns_));
+ // Cache footer of next stripe to avoid blocking I/O.
+ if (currentStripe_ + 1 < lastStripe_) {
+ const auto& nextStripe =
footer_->stripes(static_cast<int>(currentStripe_ + 1));
+ contents_->cacheRanges(std::vector<ReadRange>{ReadRange{
+ nextStripe.offset() + nextStripe.index_length() +
nextStripe.data_length(),
+ nextStripe.footer_length()}});
+ }
+ }
+
contents_->evictCache(currentStripeInfo_.offset());
Review Comment:
Good point!
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