Hello Will Berkeley, Kudu Jenkins, Mostafa Mokhtar,
I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/10213
to look at the new patch set (#2).
Change subject: Fast path scanning blocks of deleted rows
......................................................................
Fast path scanning blocks of deleted rows
This adds some very simple fast-paths in the case that an entire row
block consists of rows that were deleted.
The first is in the block materialization code: if delta application
results in all rows being deleted, we don't need to move forward and
materialize any columns.
The second is before serializing scan responses to the client. In this
case we don't need to loop over each column and read the selection
vector for each column. Instead we can just return immediately.
I tested this on a table where I'd inserted a few billion rows, deleted
them all, and then re-inserted them. Before the patch, a simple 'SELECT
* FROM t LIMIT 10' took 306sec. With the first optimization only, it
took about 10 seconds. With the second one as well, it took about 2.2
seconds.
There are probably more general optimizations that could be done for
sparsely-populated RowBlocks (eg where just a few rows are selected) but
they are much more complex, and it's relatively common for users to
delete large consecutive runs of rows. For example, users may use
'DELETE' all rows in a table or partition before re-adding them, or they
may delete all data corresponding to some prefix of the PK.
Change-Id: I9fa891c0f4e857ddd1f873ad4855154d078be6b8
---
M src/kudu/common/generic_iterators.cc
M src/kudu/tserver/tablet_service.cc
2 files changed, 11 insertions(+), 0 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/13/10213/2
--
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I9fa891c0f4e857ddd1f873ad4855154d078be6b8
Gerrit-Change-Number: 10213
Gerrit-PatchSet: 2
Gerrit-Owner: Todd Lipcon <[email protected]>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mostafa Mokhtar <[email protected]>
Gerrit-Reviewer: Will Berkeley <[email protected]>
