=============== Ceph s3 select =============== .. contents:: Overview -------- | The purpose of the **s3 select** engine is to create an efficient pipe between user client and storage nodes (the engine should be close as possible to storage). | It enables the selection of a restricted subset of (structured) data stored in an S3 object using an SQL-like syntax. | It also enables for higher level analytic-applications (such as SPARK-SQL), using that feature to improve their latency and throughput. | For example, an s3-object of several GB (CSV file), a user needs to extract a single column filtered by another column. | As the following query: | ``select customer-id from s3Object where age>30 and age<65;`` | Currently the whole s3-object must be retrieved from OSD via RGW before filtering and extracting data. | By "pushing down" the query into radosgw, it's possible to save a lot of network and CPU(serialization / deserialization). | **The bigger the object, and the more accurate the query, the better the performance**. Basic workflow -------------- | S3-select query is sent to RGW via `AWS-CLI `_ | It passes the authentication and permission process as an incoming message (POST). | **RGWSelectObj_ObjStore_S3::send_response_data** is the “entry point”, it handles each fetched chunk according to input object-key. | **send_response_data** is first handling the input query, it extracts the query and other CLI parameters. | Per each new fetched chunk (~4m), RGW executes an s3-select query on it. | The current implementation supports CSV objects and since chunks are randomly “cutting” the CSV rows in the middle, those broken-lines (first or last per chunk) are skipped while processing the query. | Those “broken” lines are stored and later merged with the next broken-line (belong to the next chunk), and finally processed. | Per each processed chunk an output message is formatted according to `AWS specification `_ and sent back to the client. | RGW supports the following response: ``{:event-type,records} {:content-type,application/octet-stream} {:message-type,event}``. | For aggregation queries the last chunk should be identified as the end of input, following that the s3-select-engine initiates end-of-process and produces an aggregated result. Basic functionalities ~~~~~~~~~~~~~~~~~~~~~ | **S3select** has a definite set of functionalities compliant with AWS. | The implemented software architecture supports basic arithmetic expressions, logical and compare expressions, including nested function calls and casting operators, which enables the user great flexibility. | review the below s3-select-feature-table_. Error Handling ~~~~~~~~~~~~~~ | Upon an error being detected, RGW returns 400-Bad-Request and a specific error message sends back to the client. | Currently, there are 2 main types of error. | | **Syntax error**: the s3select parser rejects user requests that are not aligned with parser syntax definitions, as | described in this documentation. | Upon Syntax Error, the engine creates an error message that points to the location of the error. | RGW sends back the error message in a specific error response. | | **Processing Time error**: the runtime engine may detect errors that occur only on processing time, for that type of | error, a different error message would describe that. | RGW sends back the error message in a specific error response. .. _s3-select-feature-table: Features Support ---------------- | Currently only part of `AWS select command `_ is implemented, table below describes what is currently supported. | The following table describes the current implementation for s3-select functionalities: +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Feature | Detailed | Example / Description | +=================================+=================+=======================================================================+ | Arithmetic operators | ^ * % / + - ( ) | select (int(_1)+int(_2))*int(_9) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | | ``%`` modulo | select count(*) from s3object where cast(_1 as int)%2 = 0; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | | ``^`` power-of | select cast(2^10 as int) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Compare operators | > < >= <= = != | select _1,_2 from s3object where (int(_1)+int(_3))>int(_5); | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | AND OR NOT | select count(*) from s3object where not (int(_1)>123 and int(_5)<200);| +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | is null | return true/false for null indication in expression | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | is not null | return true/false for null indication in expression | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator and NULL | unknown state | review null-handle_ observe how logical operator result with null. | | | | the following query return **0**. | | | | | | | | select count(*) from s3object where null and (3>2); | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Arithmetic operator with NULL | unknown state | review null-handle_ observe the results of binary operations with NULL| | | | the following query return **0**. | | | | | | | | select count(*) from s3object where (null+1) and (3>2); | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | compare with NULL | unknown state | review null-handle_ observe results of compare operations with NULL | | | | the following query return **0**. | | | | | | | | select count(*) from s3object where (null*1.5) != 3; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | missing column | unknown state | select count(*) from s3object where _1 is null; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | query is filtering rows where predicate | select count(*) from s3object where (_1 > 12 and _2 = 0) is not null; | | is returning non null results. | | | this predicate will return null | | | upon _1 or _2 is null | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | projection column | similar to | select case | | | switch/case | cast(_1 as int) + 1 | | | default | when 2 then "a" | | | | when 3 then "b" | | | | else "c" end from s3object; | | | | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | projection column | similar to | select case | | | if/then/else | when (1+1=(2+1)*3) then 'case_1' | | | | when ((4*3)=(12)) then 'case_2' | | | | else 'case_else' end, | | | | age*2 from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | ``coalesce {expression,expression ...} :: return first non-null argument`` | | | | | | select coalesce(nullif(5,5),nullif(1,1.0),age+12) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | ``nullif {expr1,expr2} ::return null in case both arguments are equal,`` | | | ``or else the first one`` | | | | | | select nullif(cast(_1 as int),cast(_2 as int)) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | ``{expression} in ( .. {expression} ..)`` | | | | | | select count(*) from s3object | | | where 'ben' in (trim(_5),substring(_1,char_length(_1)-3,3),last_name); | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | ``{expression} between {expression} and {expression}`` | | | | | | select count(*) from s3object | | | where substring(_3,char_length(_3),1) between "x" and trim(_1) | | | and substring(_3,char_length(_3)-1,1) = ":"; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | logical operator | ``{expression} like {match-pattern}`` | | | | | | select count(*) from s3object where first_name like '%de_'; | | | | | | select count(*) from s3object where _1 like \"%a[r-s]\; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | | ``{expression} like {match-pattern} escape {char}`` | | | | | logical operator | select count(*) from s3object where "jok_ai" like "%#_ai" escape "#"; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | true / false | select (cast(_1 as int)>123 = true) from s3object | | predicate as a projection | where address like '%new-york%'; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | an alias to | select (_1 like "_3_") as *likealias*,_1 from s3object | | predicate as a projection | where *likealias* = true and cast(_1 as int) between 800 and 900; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | casting operator | select cast(123 as int)%2 from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | casting operator | select cast(123.456 as float)%2 from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | casting operator | select cast('ABC0-9' as string),cast(substr('ab12cd',3,2) as int)*4 from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | casting operator | select cast(5 as bool) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | casting operator | select cast(substring('publish on 2007-01-01',12,10) as timestamp) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | non AWS casting operator | select int(_1),int( 1.2 + 3.4) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | non AWS casting operator | select float(1.2) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | not AWS casting operator | select to_timestamp('1999-10-10T12:23:44Z') from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Aggregation Function | sum | select sum(int(_1)) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Aggregation Function | avg | select avg(cast(_1 a float) + cast(_2 as int)) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Aggregation Function | min | select min( int(_1) * int(_5) ) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Aggregation Function | max | select max(float(_1)),min(int(_5)) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Aggregation Function | count | select count(*) from s3object where (int(_1)+int(_3))>int(_5); | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Timestamp Functions | extract | select count(*) from s3object where | | | | extract(year from to_timestamp(_2)) > 1950 | | | | and extract(year from to_timestamp(_1)) < 1960; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Timestamp Functions | date_add | select count(0) from s3object where | | | | date_diff(year,to_timestamp(_1),date_add(day,366, | | | | to_timestamp(_1))) = 1; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Timestamp Functions | date_diff | select count(0) from s3object where | | | | date_diff(month,to_timestamp(_1),to_timestamp(_2))) = 2; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Timestamp Functions | utcnow | select count(0) from s3object where | | | | date_diff(hours,utcnow(),date_add(day,1,utcnow())) = 24; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Timestamp Functions | to_string | select to_string( | | | | to_timestamp("2009-09-17T17:56:06.234567Z"), | | | | "yyyyMMdd-H:m:s") from s3object; | | | | | | | | ``result: "20090917-17:56:6"`` | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | substring | select count(0) from s3object where | | | | int(substring(_1,1,4))>1950 and int(substring(_1,1,4))<1960; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | substring with ``from`` negative number is valid | select substring("123456789" from -4) from s3object; | | considered as first | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | substring with ``from`` zero ``for`` out-of-bound | select substring("123456789" from 0 for 100) from s3object; | | number is valid just as (first,last) | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | trim | select trim(' foobar ') from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | trim | select trim(trailing from ' foobar ') from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | trim | select trim(leading from ' foobar ') from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | trim | select trim(both '12' from '1112211foobar22211122') from s3objects; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | lower/upper | select lower('ABcD12#$e') from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | String Functions | char_length | select count(*) from s3object where char_length(_3)=3; | | | character_length| | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Complex queries | select sum(cast(_1 as int)), | | | max(cast(_3 as int)), | | | substring('abcdefghijklm',(2-1)*3+sum(cast(_1 as int))/sum(cast(_1 as int))+1, | | | (count() + count(0))/count(0)) from s3object; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | alias support | | select int(_1) as a1, int(_2) as a2 , (a1+a2) as a3 | | | | from s3object where a3>100 and a3<300; | +---------------------------------+-----------------+-----------------------------------------------------------------------+ .. _null-handle: NULL ~~~~ | NULL is a legit value in ceph-s3select systems similar to other DB systems, i.e. systems needs to handle the case where a value is NULL. | The definition of NULL in our context, is missing/unknown, in that sense **NULL can not produce a value on ANY arithmetic operations** ( a + NULL will produce NULL value). | The Same is with arithmetic comparison, **any comparison to NULL is NULL**, i.e. unknown. | Below is a truth table contains the NULL use-case. +---------------------------------+-----------------------------+ | A is NULL | Result (NULL=UNKNOWN) | +=================================+=============================+ | NOT A | NULL | +---------------------------------+-----------------------------+ | A OR False | NULL | +---------------------------------+-----------------------------+ | A OR True | True | +---------------------------------+-----------------------------+ | A OR A | NULL | +---------------------------------+-----------------------------+ | A AND False | False | +---------------------------------+-----------------------------+ | A AND True | NULL | +---------------------------------+-----------------------------+ | A and A | NULL | +---------------------------------+-----------------------------+ s3-select function interfaces ----------------------------- Timestamp functions ~~~~~~~~~~~~~~~~~~~ | The timestamp functionalities as described in `AWS-specs `_ is fully implemented. | ``to_timestamp( string )`` : The casting operator converts string to timestamp basic type. | to_timestamp operator is able to convert the following ``YYYY-MM-DDTHH:mm:ss.SSSSSS+/-HH:mm`` , ``YYYY-MM-DDTHH:mm:ss.SSSSSSZ`` , ``YYYY-MM-DDTHH:mm:ss+/-HH:mm`` , ``YYYY-MM-DDTHH:mm:ssZ`` , ``YYYY-MM-DDTHH:mm+/-HH:mm`` , ``YYYY-MM-DDTHH:mmZ`` , ``YYYY-MM-DDT`` or ``YYYYT`` string formats into timestamp. | Where time (or part of it) is missing in the string format, zero's are replacing the missing parts. And for missing month and day, 1 is default value for them. | Timezone part is in format ``+/-HH:mm`` or ``Z`` , where the letter "Z" indicates Coordinated Universal Time (UTC). Value of timezone can range between -12:00 and +14:00. | ``extract(date-part from timestamp)`` : The function extracts date-part from input timestamp and returns it as integer. | Supported date-part : year, month, week, day, hour, minute, second, timezone_hour, timezone_minute. | ``date_add(date-part, quantity, timestamp)`` : The function adds quantity (integer) to date-part of timestamp and returns result as timestamp. It also includes timezone in calculation. | Supported data-part : year, month, day, hour, minute, second. | ``date_diff(date-part, timestamp, timestamp)`` : The function returns an integer, a calculated result for difference between 2 timestamps according to date-part. It includes timezone in calculation. | supported date-part : year, month, day, hour, minute, second. | ``utcnow()`` : return timestamp of current time. | ``to_string(timestamp, format_pattern)`` : returns a string representation of the input timestamp in the given input string format. to_string parameters ~~~~~~~~~~~~~~~~~~~~ +--------------+-----------------+-----------------------------------------------------------------------------------+ | Format | Example | Description | +==============+=================+===================================================================================+ | yy | 69 | 2-digit year | +--------------+-----------------+-----------------------------------------------------------------------------------+ | y | 1969 | 4-digit year | +--------------+-----------------+-----------------------------------------------------------------------------------+ | yyyy | 1969 | Zero-padded 4-digit year | +--------------+-----------------+-----------------------------------------------------------------------------------+ | M | 1 | Month of year | +--------------+-----------------+-----------------------------------------------------------------------------------+ | MM | 01 | Zero-padded month of year | +--------------+-----------------+-----------------------------------------------------------------------------------+ | MMM | Jan | Abbreviated month year name | +--------------+-----------------+-----------------------------------------------------------------------------------+ | MMMM | January | Full month of year name | +--------------+-----------------+-----------------------------------------------------------------------------------+ | MMMMM | J | Month of year first letter (NOTE: not valid for use with to_timestamp function) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | d | 2 | Day of month (1-31) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | dd | 02 | Zero-padded day of month (01-31) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | a | AM | AM or PM of day | +--------------+-----------------+-----------------------------------------------------------------------------------+ | h | 3 | Hour of day (1-12) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | hh | 03 | Zero-padded hour of day (01-12) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | H | 3 | Hour of day (0-23) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | HH | 03 | Zero-padded hour of day (00-23) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | m | 4 | Minute of hour (0-59) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | mm | 04 | Zero-padded minute of hour (00-59) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | s | 5 | Second of minute (0-59) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | ss | 05 | Zero-padded second of minute (00-59) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | S | 0 | Fraction of second (precision: 0.1, range: 0.0-0.9) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | SS | 6 | Fraction of second (precision: 0.01, range: 0.0-0.99) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | SSS | 60 | Fraction of second (precision: 0.001, range: 0.0-0.999) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | SSSSSS | 60000000 | Fraction of second (maximum precision: 1 nanosecond, range: 0.0-0999999999) | +--------------+-----------------+-----------------------------------------------------------------------------------+ | n | 60000000 | Nano of second | +--------------+-----------------+-----------------------------------------------------------------------------------+ | X | +07 or Z | Offset in hours or "Z" if the offset is 0 | +--------------+-----------------+-----------------------------------------------------------------------------------+ | XX or XXXX| +0700 or Z | Offset in hours and minutes or "Z" if the offset is 0 | +--------------+-----------------+-----------------------------------------------------------------------------------+ | XXX or XXXXX | +07:00 or Z | Offset in hours and minutes or "Z" if the offset is 0 | +--------------+-----------------+-----------------------------------------------------------------------------------+ | X | 7 | Offset in hours | +--------------+-----------------+-----------------------------------------------------------------------------------+ | xx or xxxx | 700 | Offset in hours and minutes | +--------------+-----------------+-----------------------------------------------------------------------------------+ | xxx or xxxxx | +07:00 | Offset in hours and minutes | +--------------+-----------------+-----------------------------------------------------------------------------------+ Aggregation functions ~~~~~~~~~~~~~~~~~~~~~ | ``count()`` : return integer according to number of rows matching condition(if such exist). | ``sum(expression)`` : return a summary of expression per all rows matching condition(if such exist). | ``avg(expression)`` : return a average of expression per all rows matching condition(if such exist). | ``max(expression)`` : return the maximal result for all expressions matching condition(if such exist). | ``min(expression)`` : return the minimal result for all expressions matching condition(if such exist). String functions ~~~~~~~~~~~~~~~~ | ``substring(string,from,to)`` : substring( string ``from`` start [ ``for`` length ] ) | return a string extract from input string according to from,to inputs. | ``substring(string from )`` | ``substring(string from for)`` | ``char_length`` : return a number of characters in string (``character_length`` does the same). | ``trim`` : trim ( [[``leading`` | ``trailing`` | ``both`` remove_chars] ``from``] string ) | trims leading/trailing(or both) characters from target string, the default is blank character. | ``upper\lower`` : converts characters into lowercase/uppercase. Alias ~~~~~ | **Alias** programming-construct is an essential part of s3-select language, it enables much better programming especially with objects containing many columns or in the case of complex queries. | Upon parsing the statement containing alias construct, it replaces alias with reference to correct projection column, on query execution time the reference is evaluated as any other expression. | There is a risk that self(or cyclic) reference may occur causing stack-overflow(endless-loop), for that concern upon evaluating an alias, it is validated for cyclic reference. | Alias also maintains result-cache, meaning upon using the same alias more than once, it’s not evaluating the same expression again(it will return the same result),instead it uses the result from cache. | Of Course, per each new row the cache is invalidated. Testing ~~~~~~~ | s3select contains several testing frameworks which provide a large coverage for its functionalities. | (1) tests comparison against a trusted engine, meaning, C/C++ compiler is a trusted expression evaluator, | since the syntax for arithmetical and logical expressions are identical (s3select compare to C) | the framework runs equal expressions and validates their results. | A dedicated expression generator produces different sets of expressions per each new test session. | (2) compare results of queries whose syntax is different but semantically they are equal. | this kind of test validates that different runtime flows produce an identical result, | on each run with a different dataset(random). | For one example, on a dataset which contains a random numbers(1-1000) | the following queries will produce identical results. | ``select count(*) from s3object where char_length(_3)=3;`` | ``select count(*) from s3object where cast(_3 as int)>99 and cast(_3 as int)<1000;`` | (3) constant dataset, the conventional way of testing. A query is processing a constant dataset, its result is validated against constant results. Additional syntax support ~~~~~~~~~~~~~~~~~~~~~~~~~ | S3select syntax supports table-alias ``select s._1 from s3object s where s._2 = ‘4’;`` | | S3select syntax supports case insensitive ``Select SUM(Cast(_1 as int)) FROM S3Object;`` | | S3select syntax supports statements without closing semicolon ``select count(*) from s3object`` Sending Query to RGW -------------------- | Any http-client can send an s3-select request to RGW, it must be compliant with `AWS Request syntax `_. | Sending s3-select request to RGW using AWS CLI, should follow `AWS command reference `_. | below is an example of it. :: aws --endpoint-url http://localhost:8000 s3api select-object-content --bucket {BUCKET-NAME} --expression-type 'SQL' --input-serialization '{"CSV": {"FieldDelimiter": "," , "QuoteCharacter": "\"" , "RecordDelimiter" : "\n" , "QuoteEscapeCharacter" : "\\" , "FileHeaderInfo": "USE" }, "CompressionType": "NONE"}' --output-serialization '{"CSV": {"FieldDelimiter": ":", "RecordDelimiter":"\t", "QuoteFields": "ALWAYS"}}' --key {OBJECT-NAME} --request-progress '{"Enabled": True}' --expression "select count(0) from s3object where int(_1)<10;" output.csv Input Serialization ~~~~~~~~~~~~~~~~~~~ | **FileHeaderInfo** -> (string) | Describes the first line of input. Valid values are: | | **NONE** : The first line is not a header. | **IGNORE** : The first line is a header, but you can't use the header values to indicate the column in an expression. | it's possible to use column position (such as _1, _2, …) to indicate the column (``SELECT s._1 FROM S3OBJECT s``). | **USE** : First line is a header, and you can use the header value to identify a column in an expression (``SELECT column_name FROM S3OBJECT``). | | **QuoteEscapeCharacter** -> (string) | A single character used for escaping the quotation mark character inside an already escaped value. | | **RecordDelimiter** -> (string) | A single character is used to separate individual records in the input. Instead of the default value, you can specify an arbitrary delimiter. | | **FieldDelimiter** -> (string) | A single character is used to separate individual fields in a record. You can specify an arbitrary delimiter. Output Serialization ~~~~~~~~~~~~~~~~~~~~ | **AWS CLI example** | aws s3api select-object-content \ | --bucket "mybucket" \ | --key keyfile1 \ | --expression "SELECT * FROM s3object s" \ | --expression-type 'SQL' \ | --request-progress '{"Enabled": false}' \ | --input-serialization '{"CSV": {"FieldDelimiter": ","}, "CompressionType": "NONE"}' \ | --output-serialization '{"CSV": {"FieldDelimiter": ":", "RecordDelimiter":"\\t", "QuoteFields": "ALWAYS"}}' /dev/stdout | | **QuoteFields** -> (string) | Indicates whether to use quotation marks around output fields. | **ALWAYS**: Always use quotation marks for output fields. | **ASNEEDED** (not implemented): Use quotation marks for output fields when needed. | | **RecordDelimiter** -> (string) | A single character is used to separate individual records in the output. Instead of the default value, you can specify an | arbitrary delimiter. | | **FieldDelimiter** -> (string) | The value used to separate individual fields in a record. You can specify an arbitrary delimiter. CSV parsing behavior -------------------- | s3-select engine contains a CSV parser, which parses s3-objects as follows. | - each row ends with row-delimiter. | - field-separator separates between adjacent columns, successive field separator defines NULL column. | - quote-character overrides field separator, meaning, field separator becomes as any character between quotes. | - escape character disables any special characters, except for row delimiter. | Below are examples of CSV parsing rules. +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Feature | Description | input ==> tokens | +=================================+=================+=======================================================================+ | NULL | successive | ,,1,,2, ==> {null}{null}{1}{null}{2}{null} | | | field delimiter | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | QUOTE | quote character | 11,22,"a,b,c,d",last ==> {11}{22}{"a,b,c,d"}{last} | | | overrides | | | | field delimiter | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | Escape | escape char | 11,22,str=\\"abcd\\"\\,str2=\\"123\\",last | | | overrides | ==> {11}{22}{str="abcd",str2="123"}{last} | | | meta-character. | | | | escape removed | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | row delimiter | no close quote, | 11,22,a="str,44,55,66 | | | row delimiter is| ==> {11}{22}{a="str,44,55,66} | | | closing line | | +---------------------------------+-----------------+-----------------------------------------------------------------------+ | csv header info | FileHeaderInfo | "**USE**" value means each token on first line is column-name, | | | tag | "**IGNORE**" value means to skip the first line | +---------------------------------+-----------------+-----------------------------------------------------------------------+ BOTO3 ----- | using BOTO3 is "natural" and easy due to AWS-cli support. :: import pprint def run_s3select(bucket,key,query,column_delim=",",row_delim="\n",quot_char='"',esc_char='\\',csv_header_info="NONE"): s3 = boto3.client('s3', endpoint_url=endpoint, aws_access_key_id=access_key, region_name=region_name, aws_secret_access_key=secret_key) result = "" try: r = s3.select_object_content( Bucket=bucket, Key=key, ExpressionType='SQL', InputSerialization = {"CSV": {"RecordDelimiter" : row_delim, "FieldDelimiter" : column_delim,"QuoteEscapeCharacter": esc_char, "QuoteCharacter": quot_char, "FileHeaderInfo": csv_header_info}, "CompressionType": "NONE"}, OutputSerialization = {"CSV": {}}, Expression=query, RequestProgress = {"Enabled": progress}) except ClientError as c: result += str(c) return result for event in r['Payload']: if 'Records' in event: result = "" records = event['Records']['Payload'].decode('utf-8') result += records if 'Progress' in event: print("progress") pprint.pprint(event['Progress'],width=1) if 'Stats' in event: print("Stats") pprint.pprint(event['Stats'],width=1) if 'End' in event: print("End") pprint.pprint(event['End'],width=1) return result run_s3select( "my_bucket", "my_csv_object", "select int(_1) as a1, int(_2) as a2 , (a1+a2) as a3 from s3object where a3>100 and a3<300;") S3 SELECT Responses ------------------- Error Response ~~~~~~~~~~~~~~ | | | NoSuchKey | The resource you requested does not exist | /mybucket/myfoto.jpg | 4442587FB7D0A2F9 | Report Response ~~~~~~~~~~~~~~~ | HTTP/1.1 200 | | | | blob | | |
| long | long | long |
| | |
| long | long | long |
| | | | | | Response Description ~~~~~~~~~~~~~~~~~~~~ | For CEPH S3 Select, responses can be messages of the following types: | | **Records message**: Can contain a single record, partial records, or multiple records. Depending on the size of the result, a response can contain one or more of these messages. | | **Error message**: Upon an error being detected, RGW returns 400 Bad Request, and a specific error message sends back to the client, according to its type. | | **Continuation message**: Ceph S3 periodically sends this message to keep the TCP connection open. | These messages appear in responses at random. The client must detect the message type and process it accordingly. | | **Progress message**: Ceph S3 periodically sends this message if requested. It contains information about the progress of a query that has started but has not yet been completed. | | **Stats message**: Ceph S3 sends this message at the end of the request. It contains statistics about the query. | | **End message**: Indicates that the request is complete, and no more messages will be sent. You should not assume that request is complete until the client receives an End message.