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https://issues.apache.org/jira/browse/HBASE-16888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15601740#comment-15601740
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Anoop Sam John commented on HBASE-16888:
----------------------------------------
Understood..
So now we would end up copying tags in original cell which the TagRewriteCell
wraps. The patch makes it such that we will avoid that. But now we will not
copy the tags in TagRewriteCell as such but the patch will make it to copy.
bq.return new TagRewriteCell(clonedBaseCell, this.tags);
Actually speaking we will not be having tags in the original cell what we
receive. Its different CPs and internal code path adds up tags.
TagRewriteCell constructor
{code}
this.cell = cell;
this.tags = tags;
// tag offset will be treated as 0 and length this.tags.length
if (this.cell instanceof TagRewriteCell) {
// Cleaning the ref so that the byte[] can be GCed
((TagRewriteCell) this.cell).tags = null;
}
{code}
We can do a bit of change here.
When the wrapping cell is also a TagRewriteCell we can gets its wrapped
instance and make it this.cell. I mean doing this
{code}
if (this.cell instanceof TagRewriteCell) {
this.cell = ((TagRewriteCell) cell).cell;
} else {
this.cell = cell;
}
{code}
What this is doing is even if we have N levels of TagRewriteCells, the top most
originally refer to the bottom most one which might in all chance dont have any
cells in it. Is that better than copying the current TagRewriteCell's tags
bytes?
> Avoid unnecessary tags copy in Append
> -------------------------------------
>
> Key: HBASE-16888
> URL: https://issues.apache.org/jira/browse/HBASE-16888
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 2.0.0
> Reporter: ChiaPing Tsai
> Assignee: ChiaPing Tsai
> Priority: Minor
> Fix For: 2.0.0
>
> Attachments: HBASE-16888.v0.patch
>
>
> a) If the delta has tags and the mutation doesn’t apply the TTL, we shouldn’t
> create the TagRewriteCell.
> {noformat}
> List<Tag> tags = TagUtil.carryForwardTags(delta);
> long ts = now;
> Cell newCell = null;
> byte [] row = mutation.getRow();
> if (currentValue != null) {
> ...
> } else {
> // Append's KeyValue.Type==Put and ts==HConstants.LATEST_TIMESTAMP
> CellUtil.updateLatestStamp(delta, now);
> newCell = delta;
> tags = TagUtil.carryForwardTTLTag(tags, mutation.getTTL());
> if (tags != null) {
> newCell = CellUtil.createCell(delta, tags);
> }
> }
> {noformat}
> b) If the cell has tags, the ShareableMemoryTagRewriteCell will make
> duplicate copy of tags.
> {noformat}
> Cell clonedBaseCell = ((ShareableMemory) this.cell).cloneToCell();
> return new TagRewriteCell(clonedBaseCell, this.tags);
> {noformat}
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