Thread: Postgres delete performance problem
Hi,
I have a Java application that tries to synchronize tables in two databases (remote source to local target). It does so by removing all constraints, then it compares table contents row by row, inserts missing rows and deletes "extra" rows in the target database. Delete performance is incredibly bad: it handles 100 record deletes in about 16 to 20 seconds(!). Insert and update performance is fine.
The Java statement to handle the delete uses a prepared statement:
"delete from xxx where xxx_pk=?"
The delete statement is then executed using addBatch() and executeBatch() (the latter every 100 deletes), and committed. Not using executeBatch makes no difference.
An example table where deletes are slow:
pzlnew=# \d cfs_file
Table "public.cfs_file"
Column | Type | Modifiers
------------------+-----------------------------+-----------
cfsid | bigint | not null
cfs_date_created | timestamp without time zone | not null
cfs_name | character varying(512) | not null
cfs_cfaid | bigint |
cfs_cfdid | bigint |
Indexes:
"cfs_file_pkey" PRIMARY KEY, btree (cfsid)
with no FK constraints at all, and a table size of 940204 rows.
While deleting, postgres takes 100% CPU all of the time.
Inserts and updates are handled in exactly the same way, and these are a few orders of magnitude faster than the deletes.
I am running the DB on an Ubuntu 12.04 - 64bits machine with Postgres 9.1, the machine is a fast machine with the database on ssd, ext4, with 16GB of RAM and a i7-3770 CPU @ 3.40GHz.
Anyone has any idea?
Thanks in advance,
Frits
Hello. This may be wrong type for parameter, like using setObject(param, value) instead of setObject(param, value, type). Especially if value passed is string object. AFAIR index may be skipped in this case. You can check by changing statement to "delete from xxx where xxx_pk=?::bigint". If it works, check how parameter is set in java code. 25.06.12 18:42, Frits Jalvingh написав(ла): > Hi, > > I have a Java application that tries to synchronize tables in two > databases (remote source to local target). It does so by removing all > constraints, then it compares table contents row by row, inserts > missing rows and deletes "extra" rows in the target database. Delete > performance is incredibly bad: it handles 100 record deletes in about > 16 to 20 seconds(!). Insert and update performance is fine. > > The Java statement to handle the delete uses a prepared statement: > > "delete from xxx where xxx_pk=?" > > The delete statement is then executed using addBatch() and > executeBatch() (the latter every 100 deletes), and committed. Not > using executeBatch makes no difference. > > An example table where deletes are slow: > > pzlnew=# \d cfs_file > Table "public.cfs_file" > Column | Type | Modifiers > ------------------+-----------------------------+----------- > cfsid | bigint | not null > cfs_date_created | timestamp without time zone | not null > cfs_name | character varying(512) | not null > cfs_cfaid | bigint | > cfs_cfdid | bigint | > Indexes: > "cfs_file_pkey" PRIMARY KEY, btree (cfsid) > > with no FK constraints at all, and a table size of 940204 rows. > > While deleting, postgres takes 100% CPU all of the time. > > > Inserts and updates are handled in exactly the same way, and these are > a few orders of magnitude faster than the deletes. > > I am running the DB on an Ubuntu 12.04 - 64bits machine with Postgres > 9.1, the machine is a fast machine with the database on ssd, ext4, > with 16GB of RAM and a i7-3770 CPU @ 3.40GHz. > > Anyone has any idea? > > Thanks in advance, > > Frits >
"It does so by removing all constraints, then it compares table contents row by row, inserts missing rows and deletes "extra" rows in the target database."
If the delete's you do when the constraints and indexes are removed then you need to create the constraints and indexes before you delete the rows
De: Frits Jalvingh <jal@etc.to>
Para: pgsql-performance@postgresql.org
Enviado: Lunes 25 de junio de 2012 10:42
Asunto: [PERFORM] Postgres delete performance problemHi,I have a Java application that tries to synchronize tables in two databases (remote source to local target). It does so by removing all constraints, then it compares table contents row by row, inserts missing rows and deletes "extra" rows in the target database. Delete performance is incredibly bad: it handles 100 record deletes in about 16 to 20 seconds(!). Insert and update performance is fine.The Java statement to handle the delete uses a prepared statement:"delete from xxx where xxx_pk=?"The delete statement is then executed using addBatch() and executeBatch() (the latter every 100 deletes), and committed. Not using executeBatch makes no difference.An example table where deletes are slow:pzlnew=# \d cfs_fileTable "public.cfs_file"Column | Type | Modifiers------------------+-----------------------------+-----------cfsid | bigint | not nullcfs_date_created | timestamp without time zone | not nullcfs_name | character varying(512) | not nullcfs_cfaid | bigint |cfs_cfdid | bigint |Indexes:"cfs_file_pkey" PRIMARY KEY, btree (cfsid)with no FK constraints at all, and a table size of 940204 rows.While deleting, postgres takes 100% CPU all of the time.Inserts and updates are handled in exactly the same way, and these are a few orders of magnitude faster than the deletes.I am running the DB on an Ubuntu 12.04 - 64bits machine with Postgres 9.1, the machine is a fast machine with the database on ssd, ext4, with 16GB of RAM and a i7-3770 CPU @ 3.40GHz.Anyone has any idea?Thanks in advance,Frits
Hello, Just wondering whether you were able to resolve this issue. We are experiencing a very similar issue with deletes using Postgrs 9.0.5 on Ubuntu 12.04. Dan -- View this message in context: http://postgresql.1045698.n5.nabble.com/Postgres-delete-performance-problem-tp5714153p5738765.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com.
Yes, the issue was resolved by the method I proposed. You need to specify correct type either on java-side or server-side (query text).
The driver does not parse your query, so it simply passes everything to server.
Server use widening conversion, so "bigint=number" becomes "bigint::number=number", not "bigint=number::bigint" and index can't be used when any function is applied to indexed field.
Note, that server can't do "bigint=number::bigint" because it does not know the numbers you will pass.
Consider examples:
1) 0 = 123456789012345678901234567890
2) 0 = 0.4
Correct value is false, but "bigint=number::bigint" will give you "overflow" error for the first example and true for the second, which is incorrect.
See my explanation (it seems it got out of the list):
The driver does not parse your query, so it simply passes everything to server.
Server use widening conversion, so "bigint=number" becomes "bigint::number=number", not "bigint=number::bigint" and index can't be used when any function is applied to indexed field.
Note, that server can't do "bigint=number::bigint" because it does not know the numbers you will pass.
Consider examples:
1) 0 = 123456789012345678901234567890
2) 0 = 0.4
Correct value is false, but "bigint=number::bigint" will give you "overflow" error for the first example and true for the second, which is incorrect.
2013/1/4 dankogan <dan@iqtell.com>
Hello,
Just wondering whether you were able to resolve this issue.
We are experiencing a very similar issue with deletes using Postgrs 9.0.5 on
Ubuntu 12.04.
Dan
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