UnInvertedField performance improvement on fields with an extremely large
number of values
------------------------------------------------------------------------------------------
Key: SOLR-1220
URL: https://issues.apache.org/jira/browse/SOLR-1220
Project: Solr
Issue Type: Improvement
Components: search
Affects Versions: 1.4
Reporter: Kent Fitch
Priority: Minor
Our setup is :
- about 34M lucene documents of bibliographic and full text content
- index currently 115GB, will at least double over next 6 months
- moving to support real-time-ish updates (maybe 5 min delay)
We facet on 8 fields, 6 of which are "normal" with small numbers of
distinct values. But 2 faceted fields, creator and subject, are huge,
with 18M and 9M terms respectively.
On a server with 2xquad core AMD 2382 processors and 64GB memory, java
1.6.0_13-b03, 64 bit run with "-Xmx15192M -Xms6000M -verbose:gc", with
the index on Intel X25M SSD, on start-up the elapsed time to create
the 8 facets is 306 seconds (best time). Following an index reopen,
the time to recreate them in 318 seconds (best time).
[We have made an independent experimental change to create the facets
with 3 async threads, that is, in parallel, and also to decouple them
from the underlying index, so our facets lag the index changes by the
time to recreate the facets. With our setup, the 3 threads reduced
facet creation elapsed time from about 450 secs to around 320 secs,
but this will depend a lot on IO capabilities of the device containing
the index, amount of file system caching, load, etc]
Anyway, we noticed that huge amounts of garbage were being collected
during facet generation of the creator and subject fields, and tracked
it down to this decision in UnInvertedField univert():
if (termNum >= maxTermCounts.length) {
// resize, but conserve memory by not doubling
// resize at end??? we waste a maximum of 16K (average of 8K)
int[] newMaxTermCounts = new int[maxTermCounts.length+4096];
System.arraycopy(maxTermCounts, 0, newMaxTermCounts, 0, termNum);
maxTermCounts = newMaxTermCounts;
}
So, we tried the obvious thing:
- allocate 10K terms initially, rather than 1K
- extend by doubling the current size, rather than adding a fixed 4K
- free unused space at the end (but only if unused space is
"significant") by reallocating the array to the exact required size
And also:
- created a static HashMap lookup keyed on field name which remembers
the previous allocated size for maxTermCounts for that field, and
initially allocates that size + 1000 entries
The second change is a minor optimisation, but the first change, by
eliminating thousands of array reallocations and copies, greatly
improved load times, down from 306 to 124 seconds on the initial load
and from 318 to 134 seconds on reloads after index updates. About
60-70 secs is still spend in GC, but it is a significant improvement.
Unless you have very large numbers of facet values, this change won't
have any positive benefit.
The core part of our change is reflected by this diff against revision 785058:
***************
*** 222,232 ****
int termNum = te.getTermNumber();
if (termNum >= maxTermCounts.length) {
! // resize, but conserve memory by not doubling
! // resize at end??? we waste a maximum of 16K (average of 8K)
! int[] newMaxTermCounts = new int[maxTermCounts.length+4096];
System.arraycopy(maxTermCounts, 0, newMaxTermCounts, 0, termNum);
maxTermCounts = newMaxTermCounts;
}
--- 222,232 ----
int termNum = te.getTermNumber();
if (termNum >= maxTermCounts.length) {
! // resize by doubling - for very large number of unique terms,
expanding
! // by 4K and resultant GC will dominate uninvert times. Resize at
end if material
! int[] newMaxTermCounts = new int[maxTermCounts.length*2];
System.arraycopy(maxTermCounts, 0, newMaxTermCounts, 0, termNum);
maxTermCounts = newMaxTermCounts;
}
***************
*** 331,338 ****
--- 331,346 ----
numTermsInField = te.getTermNumber();
te.close();
+ // free space if outrageously wasteful (tradeoff memory/cpu)
+
+ if ((maxTermCounts.length - numTermsInField) > 1024) { // too much waste!
+ int[] newMaxTermCounts = new int[numTermsInField];
+ System.arraycopy(maxTermCounts, 0, newMaxTermCounts, 0,
numTermsInField);
+ maxTermCounts = newMaxTermCounts;
+ }
+
long midPoint = System.currentTimeMillis();
if (termInstances == 0) {
// we didn't invert anything
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
