Questions tagged [hashing]

For questions about the usage of hashing in a database context

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Execution plan showing high hash match

i have a sql query running from database 1 that joins table company on to a view SELECT DISTINCT RTRIM([K].[cmpCompanyCode]) AS [cmpCompanyCode] FROM [dbo].[view] AS [K] JOIN [database2].[dbo].[...
deanpillow's user avatar
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1 answer
107 views

Computing hashes in PostgreSQL for JSONB columns

From PostgreSQL docs: jsonb does not preserve white space, does not preserve the order of object keys, and does not keep duplicate object keys. If duplicate keys are specified in the input, only the ...
VIAGC's user avatar
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Generating MD5 Hash for NVARCHAR and VARCHAR columns across different databases

I am building a utility that generates a single MD5 hash across all CONCATENATED column values for any table row. To make this work, I have to eliminate NULL values using COALESCE and must CAST NUMBER ...
Lauren_G's user avatar
2 votes
1 answer
1k views

Create Postgres hash aggregate function

Postgres: 15.1 My goal is simple: I want to create an aggregated hash value for x rows from column c in table z. Example Input: SELECT hash_agg(c) AS checksum FROM z; Example Output: checksum ...
Yuki's user avatar
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Issue with hash storage resulting from password_verify() output

Consider the following code: $random_token = random_bytes(32); $token_hash = password_hash( $random_token, PASSWORD_DEFAULT ); $token_base64 = sodium_bin2base64( $random_token, ...
DevelJoe's user avatar
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Application Role - Reset Password using hash or Encryption form

I need to automate reset password of database application role. Password must be encrypted or hash form due to security reason. I tried to convert password in hash form using 'Hashbytes' as mentioned ...
SQLHoncho's user avatar
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184 views

How exactly are the password hashing functions in the pgcrypto module different from the regular MD5 and other algorithms?

This is not technically a database question, but about the innards of Postgres's pgcrypto extension.The documentation says The algorithms in crypt() differ from the usual MD5 or SHA1 hashing ...
ahron's user avatar
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Looking for file-based DB engine alternative to MS Access

My company has been chained to this MS Access '97 .MDB format we've had since the dawn of time. Our schema is hierarchical, with multiple one-to-many relationships. We are at a point where we are ...
Kate M's user avatar
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1 vote
2 answers
61 views

Concurrency Control B-Tree between Hash

I am new to transaction. When I read the book "Transactional Information Systems", it is mentioned that B-tree uses key-range locking to guarantee serializability. Is that true all accesses ...
GenGG's user avatar
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1 vote
1 answer
550 views

HASHBYTES() result of another HASHBYTES(), OR CHECKSUM_AGG() aggregate for HASHBYTES()?

I want to aggregate a single HASHBYTES() from the results of another HASHBYTES()... something like CHECKSUM_AGG() does for CHECKSUM()... I have been able find how to make a single HASH per row of ...
Ricky Lively's user avatar
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Cache Hit Rate decrease postgres

On one of our servers, I found a problem: for the last three months, this indicator has been steadily decreasing, already from 95% to 89%. With what it can be connected? How to understand which ...
AlexandrT's user avatar
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2 answers
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SQL Server - Finding Parent Source from T-SQL Snippet

The environments for which I'm responsible have some pretty substantial plan non-reuse challenges. I've run across the following query (h/t Brent Ozar blog commenter Michael J Swart) that does a fine ...
AccidentalDBA_CO's user avatar
3 votes
1 answer
855 views

Why does an index on the join predicate does not improve the performance of a hash join?

Various references, such as join-strategies-and-performance-in-postgresql, say that an index on the join predicate does not improve the performance of a hash join. However, couldn't a B+ tree index ...
keezar's user avatar
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1 answer
953 views

Oracle generating hash_val from a clob

I have the following table, where I would like the value of hash_val to be generated from clob_val whether clob_val is inserted or updated. Can this be done perhaps by making the column hash_val a ...
Pugzly's user avatar
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2 answers
800 views

Postgresql 12 Custom Hash Function

I have a large table that I would like to partition. The field I want to partition against is a string that contains a coded value, but appears as an integer stored as a string. The "number" ...
techdude1996's user avatar
3 votes
1 answer
2k views

PostgreSQL: what are purpose of functions uuid_hash(uuid) and uuid_hash_extended(uuid, bigint)

Functions uuid_hash and uuid_hash_extended Exploring postgresql I discovered 2 functions that looks interesting: SELECT p.proname , obj_description(p.oid) AS func_desc, ...
Alex Yu's user avatar
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1 answer
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Several Postgres partitioning questions (hierarchical partitioning, HASH, PK order)

I'm pretty new to Postgres and to RDBMS partitioning. I have a few related questions about the performance benefits of partitioning. Background: I am trying to fix slow batch queries on a 4 column ...
Stephen's user avatar
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4 votes
1 answer
237 views

In PostgreSQL, what area in memory does HashSetOp use, work_mem or shared_buffer?

I want to know the difference between the hash table in a hash join and the hash table in HashSetOp Except. Here is the PostgreSQL script I wrote to explain my question. drop table if exists t1 ...
JAEGEUN YU's user avatar
3 votes
0 answers
558 views

Recent degradation/variability of HashBytes performance

Up until a few days ago, T-SQL code we have running in SQL Azure that generates an MD5 for temp table values was fast (a few seconds per hundred thousand on a Business Critical Gen 5, 2 VCores DB). ...
Vince's user avatar
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3 votes
2 answers
718 views

Conflict resolution for hash-backed unique constraint of large text bodies

So we've just run into ERROR: index row size 2736 exceeds maximum 2712 for index "foo__bar__un" Hint: Values larger than 1/3 of a buffer page cannot be indexed. Consider a function index ...
User1291's user avatar
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1 answer
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Is there a cross-platform way to compare data in one columnd on each sitde of replicated data, like a checksum or hash?

I have an Oracle 12 database with lots of tables, and I am replicating several of the tables (a subset of rows) into a SQL Server 2016 database. The subset of rows can be established with a WHERE ...
Patrick Szalapski's user avatar
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1 answer
1k views

How to create automatic partitions on a non-time based column in Postgres?

I want to create a partition on a column which is of type serial. A hash based partition seems appropriate here. But from what I understand I will need to create all the partitions myself (based on ...
Ashwin's user avatar
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1 answer
552 views

Does Oracle guarentee that ORA_HASH is used to determine which hash partition a row is inserted, and will this be honored in the future?

I use hash partitioning for a few of my very large tables, and occasionally I have a use case where it would be convenient to have a mechanism that would return the partition name that a row would be ...
Matthew Moisen's user avatar
8 votes
3 answers
8k views

Is left hash join always better than left outer join?

I have a query that runs quite slow (see below). While searching for a way to improve it we found that the query runs about ten times faster if we replaced the LEFT OUTER JOIN with LEFT HASH JOIN The ...
merger's user avatar
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4 votes
2 answers
705 views

SQL Server hashbytes seed

I'm trying to compare hashes generated by SQL Server HASHBYTES() with hashes generated with python's hash() (or hashlib) function. For both functions, the same algorithm is used. The problem is I don'...
zimek-atomek's user avatar
1 vote
2 answers
2k views

oracle - hashing method, excluding DBMS_CRYPTO

BACKGROUND: DBAs have hidden DBMS_CRYPTO package to any role, grantee, and I wonder why. I have to use wrapper instead :( Is there any way to get the same hash for the text field with the same text? ...
Jakub P's user avatar
  • 157
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3 answers
153 views

Index of which columns are NOT empty

I am trying to enhance the search performance of a table based on whether certain columns contain values. I have the following columns : id | link | text | date | lat | long | type If a record ...
Leon's user avatar
  • 103
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0 answers
239 views

Hash matches with collisions

I'm trying to improve certain matches that happen often, on many many dimension columns. So my choices as I understand are: Match on many columns Hash the columns, store the hash, match on that. If ...
Jamie Marshall's user avatar
1 vote
2 answers
3k views

MSSQL Hashbytes produces different output, string vs column value

The following SQL SELECT CONVERT(nvarchar(128), HASHBYTES ('SHA2_512', 'test'), 2) as 'From String' produces the following hash: ...
JOSEFtw's user avatar
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4 votes
2 answers
10k views

Efficient key value store in Postgres

I want to use Postgres(11 in CloudSQL) as an efficient key value store. I have about 200GB of dictionaries (average size is 10kB, the structure can be different and nested). I'm thinking about ...
Lukasz Madon's user avatar
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1 answer
723 views

How to optimize query for text array in PostgreSQL using `@>` operator

I have a column of type text[] and I want to search over this column using this SQL operator @> Note: @> operator, it filters the data as such ['a','b'] in ['a','b','c'] The ...
Fadi Bakoura's user avatar
10 votes
1 answer
470 views

Hash aggregate bailout

A question that arose in a chat discussion: I know hash join bailout switches internally to a sort of nested loops thing. What does SQL Server do for a hash aggregate bailout (if it can happen at ...
Paul White's user avatar
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1 answer
600 views

HashBytes Computed Column: Exclude Column

We want to create Hashbytes computed column Non-Persisted. Table has twenty columns, and would like to exclude IdentityId column. How could I do this in computed column? Is there a SQL library ...
user avatar
3 votes
1 answer
293 views

Definition of indexing, datatype configuration, and DBMS for SHA3-256 hashes

I am designing a system within which I will need to be able to search a database using a file or string SHA3-256 hash. For example the hash of test is ...
Matthew's user avatar
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4 votes
1 answer
3k views

Should I use the deprecated MD5 function in SQL Server?

We'd like to use MD5 for our hashing function instead of SHA_256 but as of SQL Server 2016, MD5 is deprecated. We're using this for hashing (comparing which records have changed). We now have this ...
Gabe's user avatar
  • 1,334
6 votes
2 answers
2k views

Byte ordering for multibyte characters in SQL Server versus Oracle

I am currently in the process of migrating data from Oracle to SQL Server and I'm encountering an issue trying to validate the data post-migration. Environment Details: Oracle 12 - AL32UTF8 ...
HandyD's user avatar
  • 9,932
31 votes
4 answers
3k views

What is a scalable way to simulate HASHBYTES using a SQL CLR scalar function?

As part of our ETL process, we compare rows from staging against the reporting database to figure out if any of the columns have actually changed since the data was last loaded. The comparison is ...
Joe Obbish's user avatar
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11 votes
1 answer
2k views

What is the algorithm behind the EXCEPT operator?

What is the internal algorithm of how the Except operator works under the covers in SQL Server? Does it internally take a hash of each row and compare? David Lozinksi ran a study, SQL: Fastest way to ...
user avatar
1 vote
1 answer
641 views

Specify build and probe tables to hash join?

I am observing a situation in AdventureWorks database where the hash join operator is building hash table using a larger input (296 rows) and then probing with a much smaller input (3 rows). I'm not ...
upInCloud's user avatar
  • 113
17 votes
3 answers
13k views

How is it possible for Hash Index not to be faster than Btree for equality lookups?

For every version of Postgres that supported hash indexing, there is a warning or note that hash indexes are "similar or slower" or "not better" than btree indexes, at least up to version 8.3. From ...
Sampson Crowley's user avatar
0 votes
1 answer
2k views

How to convert hex chars to byte array in mysql

Got sha1 checksum in hexadecimal format(40 characters). Need help to convert hex chars to byte array in mysql. Thanks.
Shamsher singh rana's user avatar
0 votes
1 answer
1k views

Insert PBKDF2 hash into PostgreSQL container

I am using the PostgreSQL docker image with the following Dockerfile: FROM postgres:10.1 COPY init-db.sh /docker-entrypoint-initdb.d/init-db.sh and an init-db.sh script with the following content: ...
user2609980's user avatar
-1 votes
1 answer
2k views

Use Sha vs md5 or Hash in Snowflake-db

Let me preface by saying that I am not using this for storing passwords or any other sensitive info -- I simply want a row-level sha/hash that I can use later or to check for unique records. My tables ...
Serban Tanasa's user avatar
9 votes
1 answer
22k views

Best Data Type to Store Result of HASHBYTES('MD5', ...)

What would be the best data type to store the results of the HASHBYTES('MD5', ...)? It outputs 16 bytes of binary as follows: e.g. 0x5CFCD77F9FF836189D2F647EBCEA183E I could store it in the ...
GWR's user avatar
  • 2,807
2 votes
1 answer
853 views

SQL Server Latching from Multithreading/Parallel Inserts and Hash Partitioning

We are conducting parallel, multithreading inserts in SQL server tables, and want to reduce latching. What are the disadvantages of utilizing hash partitioning to reduce latching? Is it reduced ...
user avatar
2 votes
1 answer
4k views

MySQL passwords SHA512 using AES_ENCRYPT instead of ENCRYPT?

A tutorial is asking me to encrypt passwords using SHA512 in the following manner: INSERT INTO `vir_users` (`id`, `domain_id`, `password` , `email`) VALUES ('1', '1', ENCRYPT('pw1', CONCAT('$6$', ...
Henry van Megen's user avatar
8 votes
3 answers
2k views

Does Microsoft release its SQL Query Hash Algorithm..?

We use SQL Spotlight in our environment. it's pretty handy. we use particularly the output of sys.dm_exec_requests and sys.dm_exec_query_stats. Spotlight pulls the query plan from the plan cache for ...
g0pher's user avatar
  • 83
7 votes
1 answer
10k views

Using HASHBYTES() yields different results for nvarchar and a variable

I'm using server-side hashing to transmit passwords, then running PBKDF2 in the database to store the hashed password + salt combination. Hashing nvarchar(max) and a @variable holding the same value ...
Nate Anderson's user avatar
3 votes
0 answers
87 views

What is a cost of search for records in a table with an equality predicate on a non key attribute A and a static hash organization?

To speed up the search for records in a table with an equality predicate on a non key attribute A and selectivity factor fs, is preferable: A sequential organization on a key attribute ? A static ...
Revolucion for Monica's user avatar
1 vote
1 answer
724 views

SQL Server Query Plan Hash Collision

I'm wondering if anyone can shed light on a worry of mine that a query_plan_hash collision could cause a query to be executed as an entirely different query. The hash is a 16 digit Hex that sp_help ...
Dave Sims's user avatar
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