Wail Y. Alkowaileet created ASTERIXDB-3407:
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Summary: Increment page counter when skipping a valid page's cloud
bytes
Key: ASTERIXDB-3407
URL: https://issues.apache.org/jira/browse/ASTERIXDB-3407
Project: Apache AsterixDB
Issue Type: Bug
Components: STO - Storage
Affects Versions: 0.9.10
Reporter: Wail Y. Alkowaileet
Assignee: Wail Y. Alkowaileet
Fix For: 0.9.10
An issue was observed when testing cloud caching:
{noformat}
Failure while trying to read a page from
diskorg.apache.hyracks.api.exceptions.HyracksDataException:
java.io.IOException: FAILED_TO_UNCOMPRESS(5) {noformat}
Given the following code snippet in
[CloudMegaPageReadContext.java|https://github.com/apache/asterixdb/blob/master/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree-column/src/main/java/org/apache/hyracks/storage/am/lsm/btree/column/cloud/buffercache/read/CloudMegaPageReadContext.java]
{noformat}
@Override
public void onPin(ICachedPage page) throws HyracksDataException {
CloudCachedPage cachedPage = (CloudCachedPage) page;
if (gapStream != null && cachedPage.skipCloudStream()) {
/*
* This page is requested but the buffer cache has a valid copy in
memory. Also, the page itself was
* requested to be read from the cloud. Since this page is valid,
no buffer cache read() will be performed.
* As the buffer cache read() is also responsible for persisting
the bytes read from the cloud, we can end
* up writing the bytes of this page in the position of another
page. Therefore, we should skip the bytes
* for this particular page to avoid placing the bytes of this page
into another page's position.
*/
try {
long remaining = cachedPage.getCompressedPageSize();
while (remaining > 0) {
remaining -= gapStream.skip(remaining);
}
} catch (IOException e) {
throw HyracksDataException.create(e);
}
}
} {noformat}
The issue appeared when the following sequence is performed to read a range of
columnar pages
1- Reading N valid pages from the buffer cache
2- Doing a read of a page that requires to be retrieved from the cloud. A
stream will be created. However,
[pageCounter|https://github.com/apache/asterixdb/blob/7b3f1eb481a54119529d1372df148468613dd69e/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree-column/src/main/java/org/apache/hyracks/storage/am/lsm/btree/column/cloud/buffercache/read/CloudMegaPageReadContext.java#L53]
was never incremented when the N valid pages where pinned.
3- The created stream will start from the page that requires to be read from
the cloud in addition to
[numberOfContiguousPages|https://github.com/apache/asterixdb/blob/7b3f1eb481a54119529d1372df148468613dd69e/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree-column/src/main/java/org/apache/hyracks/storage/am/lsm/btree/column/cloud/buffercache/read/CloudMegaPageReadContext.java#L52]
-
[pageCounter|https://github.com/apache/asterixdb/blob/7b3f1eb481a54119529d1372df148468613dd69e/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree-column/src/main/java/org/apache/hyracks/storage/am/lsm/btree/column/cloud/buffercache/read/CloudMegaPageReadContext.java#L53C17-L53C28].
The issue is
[pageCounter|https://github.com/apache/asterixdb/blob/7b3f1eb481a54119529d1372df148468613dd69e/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree-column/src/main/java/org/apache/hyracks/storage/am/lsm/btree/column/cloud/buffercache/read/CloudMegaPageReadContext.java#L53C17-L53C28]
was never incremented (i.e., it is 0). Thus, we will request more pages than
we suppose to read. This will be OK if the component has those pages. However,
if the requested range of pages exceeds the component's pages, then an
undefined behavior will occur. In the case with compressed pages, we got an
incompressible page.
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