@@ -66,7 +66,7 @@ GET /_search
66
66
--------------------------------------------------
67
67
// TEST[s/_search/_search\?filter_path=aggregations/]
68
68
69
- <1> `terms` aggregation should be a field of type `keyword` or any other data type suitable for bucket aggregations. In order to use it with `text` you will need to enable
69
+ <1> `terms` aggregation should be a field of type `keyword` or any other data type suitable for bucket aggregations. In order to use it with `text` you will need to enable
70
70
<<fielddata, fielddata>>.
71
71
72
72
Response:
@@ -124,84 +124,10 @@ NOTE: If you want to retrieve **all** terms or all combinations of terms in a ne
124
124
[[search-aggregations-bucket-terms-aggregation-approximate-counts]]
125
125
==== Document counts are approximate
126
126
127
- As described above, the document counts (and the results of any sub aggregations) in the terms aggregation are not always
128
- accurate. This is because each shard provides its own view of what the ordered list of terms should be and these are
129
- combined to give a final view. Consider the following scenario:
130
-
131
- A request is made to obtain the top 5 terms in the field product, ordered by descending document count from an index with
132
- 3 shards. In this case each shard is asked to give its top 5 terms.
133
-
134
- [source,console]
135
- --------------------------------------------------
136
- GET /_search
137
- {
138
- "aggs" : {
139
- "products" : {
140
- "terms" : {
141
- "field" : "product",
142
- "size" : 5
143
- }
144
- }
145
- }
146
- }
147
- --------------------------------------------------
148
- // TEST[s/_search/_search\?filter_path=aggregations/]
149
-
150
- The terms for each of the three shards are shown below with their
151
- respective document counts in brackets:
152
-
153
- [width="100%",cols="^2,^2,^2,^2",options="header"]
154
- |=========================================================
155
- | | Shard A | Shard B | Shard C
156
-
157
- | 1 | Product A (25) | Product A (30) | Product A (45)
158
- | 2 | Product B (18) | Product B (25) | Product C (44)
159
- | 3 | Product C (6) | Product F (17) | Product Z (36)
160
- | 4 | Product D (3) | Product Z (16) | Product G (30)
161
- | 5 | Product E (2) | Product G (15) | Product E (29)
162
- | 6 | Product F (2) | Product H (14) | Product H (28)
163
- | 7 | Product G (2) | Product I (10) | Product Q (2)
164
- | 8 | Product H (2) | Product Q (6) | Product D (1)
165
- | 9 | Product I (1) | Product J (6) |
166
- | 10 | Product J (1) | Product C (4) |
167
-
168
- |=========================================================
169
-
170
- The shards will return their top 5 terms so the results from the shards will be:
171
-
172
- [width="100%",cols="^2,^2,^2,^2",options="header"]
173
- |=========================================================
174
- | | Shard A | Shard B | Shard C
175
-
176
- | 1 | Product A (25) | Product A (30) | Product A (45)
177
- | 2 | Product B (18) | Product B (25) | Product C (44)
178
- | 3 | Product C (6) | Product F (17) | Product Z (36)
179
- | 4 | Product D (3) | Product Z (16) | Product G (30)
180
- | 5 | Product E (2) | Product G (15) | Product E (29)
181
-
182
- |=========================================================
183
-
184
- Taking the top 5 results from each of the shards (as requested) and combining them to make a final top 5 list produces
185
- the following:
186
-
187
- [width="40%",cols="^2,^2"]
188
- |=========================================================
189
-
190
- | 1 | Product A (100)
191
- | 2 | Product Z (52)
192
- | 3 | Product C (50)
193
- | 4 | Product G (45)
194
- | 5 | Product B (43)
195
-
196
- |=========================================================
197
-
198
- Because Product A was returned from all shards we know that its document count value is accurate. Product C was only
199
- returned by shards A and C so its document count is shown as 50 but this is not an accurate count. Product C exists on
200
- shard B, but its count of 4 was not high enough to put Product C into the top 5 list for that shard. Product Z was also
201
- returned only by 2 shards but the third shard does not contain the term. There is no way of knowing, at the point of
202
- combining the results to produce the final list of terms, that there is an error in the document count for Product C and
203
- not for Product Z. Product H has a document count of 44 across all 3 shards but was not included in the final list of
204
- terms because it did not make it into the top five terms on any of the shards.
127
+ Document counts (and the results of any sub aggregations) in the terms
128
+ aggregation are not always accurate. Each shard provides its own view of what
129
+ the ordered list of terms should be. These views are combined to give a final
130
+ view.
205
131
206
132
==== Shard Size
207
133
@@ -226,35 +152,7 @@ The default `shard_size` is `(size * 1.5 + 10)`.
226
152
227
153
There are two error values which can be shown on the terms aggregation. The first gives a value for the aggregation as
228
154
a whole which represents the maximum potential document count for a term which did not make it into the final list of
229
- terms. This is calculated as the sum of the document count from the last term returned from each shard. For the example
230
- given above the value would be 46 (2 + 15 + 29). This means that in the worst case scenario a term which was not returned
231
- could have the 4th highest document count.
232
-
233
- [source,console-result]
234
- --------------------------------------------------
235
- {
236
- ...
237
- "aggregations" : {
238
- "products" : {
239
- "doc_count_error_upper_bound" : 46,
240
- "sum_other_doc_count" : 79,
241
- "buckets" : [
242
- {
243
- "key" : "Product A",
244
- "doc_count" : 100
245
- },
246
- {
247
- "key" : "Product Z",
248
- "doc_count" : 52
249
- }
250
- ...
251
- ]
252
- }
253
- }
254
- }
255
- --------------------------------------------------
256
- // TESTRESPONSE[s/\.\.\.//]
257
- // TESTRESPONSE[s/: (\-)?[0-9]+/: $body.$_path/]
155
+ terms. This is calculated as the sum of the document count from the last term returned from each shard.
258
156
259
157
==== Per bucket document count error
260
158
@@ -280,39 +178,7 @@ GET /_search
280
178
281
179
This shows an error value for each term returned by the aggregation which represents the 'worst case' error in the document count
282
180
and can be useful when deciding on a value for the `shard_size` parameter. This is calculated by summing the document counts for
283
- the last term returned by all shards which did not return the term. In the example above the error in the document count for Product C
284
- would be 15 as Shard B was the only shard not to return the term and the document count of the last term it did return was 15.
285
- The actual document count of Product C was 54 so the document count was only actually off by 4 even though the worst case was that
286
- it would be off by 15. Product A, however has an error of 0 for its document count, since every shard returned it we can be confident
287
- that the count returned is accurate.
288
-
289
- [source,console-result]
290
- --------------------------------------------------
291
- {
292
- ...
293
- "aggregations" : {
294
- "products" : {
295
- "doc_count_error_upper_bound" : 46,
296
- "sum_other_doc_count" : 79,
297
- "buckets" : [
298
- {
299
- "key" : "Product A",
300
- "doc_count" : 100,
301
- "doc_count_error_upper_bound" : 0
302
- },
303
- {
304
- "key" : "Product Z",
305
- "doc_count" : 52,
306
- "doc_count_error_upper_bound" : 2
307
- }
308
- ...
309
- ]
310
- }
311
- }
312
- }
313
- --------------------------------------------------
314
- // TESTRESPONSE[s/\.\.\.//]
315
- // TESTRESPONSE[s/: (\-)?[0-9]+/: $body.$_path/]
181
+ the last term returned by all shards which did not return the term.
316
182
317
183
These errors can only be calculated in this way when the terms are ordered by descending document count. When the aggregation is
318
184
ordered by the terms values themselves (either ascending or descending) there is no error in the document count since if a shard
@@ -673,7 +539,7 @@ GET /_search
673
539
674
540
===== Filtering Values with partitions
675
541
676
- Sometimes there are too many unique terms to process in a single request/response pair so
542
+ Sometimes there are too many unique terms to process in a single request/response pair so
677
543
it can be useful to break the analysis up into multiple requests.
678
544
This can be achieved by grouping the field's values into a number of partitions at query-time and processing
679
545
only one partition in each request.
@@ -712,10 +578,10 @@ GET /_search
712
578
This request is finding the last logged access date for a subset of customer accounts because we
713
579
might want to expire some customer accounts who haven't been seen for a long while.
714
580
The `num_partitions` setting has requested that the unique account_ids are organized evenly into twenty
715
- partitions (0 to 19). and the `partition` setting in this request filters to only consider account_ids falling
581
+ partitions (0 to 19). and the `partition` setting in this request filters to only consider account_ids falling
716
582
into partition 0. Subsequent requests should ask for partitions 1 then 2 etc to complete the expired-account analysis.
717
583
718
- Note that the `size` setting for the number of results returned needs to be tuned with the `num_partitions`.
584
+ Note that the `size` setting for the number of results returned needs to be tuned with the `num_partitions`.
719
585
For this particular account-expiration example the process for balancing values for `size` and `num_partitions` would be as follows:
720
586
721
587
1. Use the `cardinality` aggregation to estimate the total number of unique account_id values
@@ -724,8 +590,8 @@ For this particular account-expiration example the process for balancing values
724
590
4. Run a test request
725
591
726
592
If we have a circuit-breaker error we are trying to do too much in one request and must increase `num_partitions`.
727
- If the request was successful but the last account ID in the date-sorted test response was still an account we might want to
728
- expire then we may be missing accounts of interest and have set our numbers too low. We must either
593
+ If the request was successful but the last account ID in the date-sorted test response was still an account we might want to
594
+ expire then we may be missing accounts of interest and have set our numbers too low. We must either
729
595
730
596
* increase the `size` parameter to return more results per partition (could be heavy on memory) or
731
597
* increase the `num_partitions` to consider less accounts per request (could increase overall processing time as we need to make more requests)
0 commit comments